What can happen with a severe cold. Rhinitis (runny nose) - types, symptoms and causes

Myth. Whether the body manages to defeat viruses on its own, without drugs, depends on immunity and many other factors. It is better not to take risks and not let everything take its course: if you do not treat a runny nose, it may well turn into sinusitis, otitis media, pharyngitis, laryngitis, it can even end in bronchitis or pneumonia.


2. You can catch a runny nose if you get cold or get your feet wet.

Myth. With good immunity, neither hypothermia nor wet feet in themselves will lead to a runny nose. But if, due to these factors, the immune system weakens, it can easily become a target for viruses that attack it.


3. Washing the nose and gargling with saline solutions help not to get sick, and if you get sick, you will recover faster

Truth. This simple procedure helps to moisturize the nasopharyngeal mucosa, strengthening its local immunity, and clears it of mucus and microbes. The main thing is not to be lazy and do it every day, at least in the morning and evening, and if you feel that you are getting sick, once an hour or two. If you start gargling and rinsing your nose at the first sign of a cold, you can quickly defeat the virus.


4. Runny nose can be chronic

Truth. A runny nose, or scientifically called rhinitis, is usually just a symptom. It all depends on the cause of the disease. And if, for example, we are talking about allergies, then this symptom can really accompany for a long time, and in some cases (for example, with a deviated nasal septum or some endocrine diseases), you can suffer from a runny nose all your life. But if we are talking about a runny nose as a symptom of a cold (that is, SARS), and it does not go away a week after the start of treatment, and the discharge has become yellow or gray, then microbes are actively multiplying in the sinuses, and this is not a chronic runny nose. Not far from sinusitis, sinusitis, etc. Urgently see a doctor!


5. To get a runny nose, you need to be sneezed on you.

Myth. If this is a symptom of SARS, an acute respiratory viral infection, then you can become infected both by airborne droplets and by direct contact with the carrier of the virus or even just his things.

6. Cold drops can be addictive.

Truth. It is not by chance that doctors advise using such remedies in the treatment of a cold only in the first 2-3 days, during acute stage when the nose is stuffed up, it pours out and it is impossible to breathe. Vasoconstrictor drops, if used for a long time, disrupt the nutrition of the nasal mucosa and vascular tone, they become more fragile. The elasticity of their walls is markedly reduced, and as a result, chronic atrophic rhinitis may occur.

Evgenia Shakhova

Doctor of Medical Sciences, Professor, Physician the highest category, Chief Otorhinolaryngologist of the Health Committee of the Administration of the Volgograd Region

Acute rhinitis is most often of viral etiology. The first period of the disease lasts from several hours to a day and is characterized by a feeling of tension, dryness in the nose. The second stage is characterized by copious discharge from the nose, congestion. At this stage, to improve breathing, it is usually used vasoconstrictor drops. But it is important to remember that without a doctor's prescription, they can only be used for a few days.


7. If you have a runny nose, it is better to refuse a handkerchief.

Both truth and myth. If we are talking about a fabric handkerchief, then this is absolutely true: after the very first use, it becomes a real breeding ground for germs. So disposable paper handkerchiefs are not only more convenient, but also more hygienic. If, from their frequent use, the skin turns red, irritated, use a softening cream or ointment with panthenol.


8. If you drip onion or garlic juice into your nose, you will quickly recover.

Myth. There is not a single serious scientific study confirming this. But in this way, you can easily earn a serious irritation of the already inflamed nasal mucosa or even burn it. It is much more useful to eat onions and garlic for food: phytoncides will help you recover faster.


9. If you warm up your nose and legs, you can get rid of a runny nose faster

Both truth and myth. In the acute stage of a runny nose, warming up the nose really helps to "dry the runny nose" - largely by improving the blood supply to the nasal mucosa and reducing swelling. But if microbes began to actively multiply in the sinuses, heat will accelerate their reproduction, and sinusitis or sinusitis may develop. That is why it is possible to warm the nose only in the initial, acute stage of the disease. As for hot foot baths, they are really useful at any stage of a cold: there are many reflex points on the soles of the feet, closely related to respiratory system and at the same time helping the immune system to cope with viruses faster.

It is difficult to find a person who at least once has not experienced what a runny nose is. The problem is ubiquitous and all people face it without limitation. But not everyone understands what processes take place in the nose and why discharge suddenly appears from it. These questions are worth considering in more detail.

The nasal cavity is covered with a mucous membrane. It consists of prismatic epithelium, equipped with cilia (ciliated), and glandular cells. This cover is densely permeated with capillaries; sensitive nerve receptors (including olfactory ones) are located in it. The morphological features of the mucous membrane are a solid basis for the functions it performs:

  • Upper respiratory protection.
  • Moisturizing and warming the air.
  • Olfaction.

Glandular cells secrete mucus, which lubricates the surface layer of the epithelium, thereby maintaining an optimal moisture regime. It contains substances that contribute to the destruction of microbes (lysozyme, interferon, lactoferrin, secretory immunoglobulins), preventing their further spread. Foreign particles, immersed in the mucous fluid, are brought out due to the movement of the cilia of the ciliated epithelium. This is how the main function is carried out - protective.


Thus, the inhaled air in the nasal cavity is cleaned, moistened and warmed. The latter circumstance is associated with intensive blood circulation in the capillaries. It is impossible not to mention that the mucous membrane has an olfactory function, allowing a person to distinguish smells. All this can be disturbed during a runny nose.

Causes and mechanisms

The medical name for the common cold is rhinitis. But its structure is quite diverse. The appearance of a pathological process on the mucous membrane is associated with inflammation, increased vascular permeability (including with allergies), and trophic disorders. Most often you have to deal with an infectious-inflammatory rhinitis. It develops under the influence of saprophytic flora, which is already contained in the nasal cavity, but is activated against the background of a decrease in local and general reactivity of the body. Contributing factors are:

  • Hypothermia.
  • Acute and chronic diseases.
  • Injuries and operations on the nose.
  • Foreign bodies, adenoids.
  • Deviation of the nasal septum.
  • Professional hazards.
  • Smoking.

With inflammation, the mucous membrane swells, a serous effusion forms in the nose, and the movement of cilia stops. The epithelium is infiltrated with cellular elements, and then desquamated with the formation of erosions. Great importance in what causes a runny nose, vascular changes are assigned. They develop under the influence of neurovegetative stimulation (stress, emotional stress, cold air, irrational use of vasoconstrictors) or upon contact with allergens:

  1. Household (dust, wool).
  2. Food (citrus fruits, chocolate, strawberries, nuts, seafood, eggs).
  3. Vegetable (pollen, fluff, smells).
  4. Chemical (paint and varnish products, perfumes and cosmetics, detergents).
  5. Medicinal (a wide range of drugs).

The sensitizing agent, hitting the mucous membrane, induces immune response reactions. It is first taken up by macrophages, which present antigenic particles to T-lymphocytes. They produce cytokines that stimulate the formation of plasma cells. And they, in turn, synthesize specific class E immunoglobulins. The latter are adsorbed on the surface of basophils and mast cells. And when there is repeated contact with the allergen, they will contact it, forming an immune complex. This will be a signal to exit the cells biologically. active substances(histamine, bradykinin, thromboxane, serotonin, etc.), which increase the permeability vascular wall and cause symptoms allergic rhinitis.

To understand why a runny nose occurs and what it is, you can only after consulting a doctor. The specialist will conduct a full diagnosis to determine the source of the problem.

Symptoms

Those who often have a runny nose know firsthand how it manifests itself. But without the intervention of a doctor is still not enough. He will conduct an in-depth assessment of existing complaints, detail them and perform a physical examination. This is necessary to build a preliminary conclusion on which further diagnostic measures are based.

Acute rhinitis

Infectious-inflammatory rhinitis begins acutely. Both halves of the nose are affected at once. Its main symptoms will be:

  • Allocations.
  • Congestion.
  • Deterioration of the general condition.

But they do not appear immediately. Flow acute rhinitis goes through three successive stages. First, the mucous membrane is irritated. It is characterized by a feeling of dryness, tickling, scratching in the nose. Meanwhile, the temperature rises, fatigue and malaise appear. In the nose, on examination, redness is determined, the injected vessels are clearly visible, but there is no discharge.


The next stage is accompanied by the formation of serous secretions. Transudate sweats from the vascular wall, so a clear liquid flows abundantly from the nose, which soon becomes mucous. Dryness is no longer a concern, but it is difficult nasal breathing. Often, signs of conjunctivitis join and lay the ears. This is due to the spread of the process to the lacrimal canaliculus and the Eustachian tube.

After about 5 days, the amount of discharge begins to decrease, it becomes thicker and acquires a yellowish-greenish tint. This is due to the penetration of leukocytes and desquamated epithelium. Nasal congestion gradually disappears, breathing is restored, normalizes general state. At protracted course rhinitis can cause sinusitis, pharyngotracheitis, otitis media.

AT childhood acute rhinitis is more severe, which is due to the physiological narrowness of the nasal passages, the imperfection of protective mechanisms, adenoid growths, the impossibility of adequate blowing. Even common cold, which appeared in an infant, can cause a high temperature, which can provoke convulsions and meningism phenomena. Babies refuse natural feeding, because they cannot suckle with a stuffy nose, get tired quickly, and are drowsy. Due to the wide and short auditory tube inflammatory process often extended to tympanic cavity(otitis).

The development of acute rhinitis goes through several stages, which are accompanied by corresponding clinical manifestations.

Specific rhinitis

A runny nose may appear against the background of common infectious diseases(usually viral). Then it has a secondary character and is called specific. With influenza, adenovirus infection, measles and other diseases, rhinitis is a constant companion of patients. Even common colds do not pass without it. AT clinical picture general manifestations will prevail:

  • Fever.
  • Body aches (muscles and joints).
  • Malaise and fatigue.
  • Headache.

In influenza, coryza with scanty serous discharge and severe nasal congestion. It appears from the first days of illness and can be combined with nosebleeds. adeno viral infection parallel accompanied by conjunctivitis, pharyngitis, enlarged lymph nodes. And with measles, against the background of catarrhal phenomena in the nasopharynx, a rash occurs on the body (maculopapular).

allergic rhinitis

Sensitization reactions cause a special runny nose - this is rhinitis of an allergic nature. It is included in the structure of vasomotor disorders, which are manifested by the following main features:

  • Paroxysmal sneezing.
  • Copious liquid discharge.
  • Itching in the nose and tickling.
  • Feeling of congestion.

With a seasonal form of exacerbation, they can appear only in the spring (during the flowering of plants), and a year-round runny nose is accompanied by permanent signs which significantly impair the quality of life of patients. In addition, rhinitis is often included in the picture of general atopy, along with bronchial asthma and pollinosis.

Chronic rhinitis

Runny nose, ongoing long time called chronic. However, morphological changes in the mucous membrane are of a different nature:

  • Edema and hyperemia.
  • Hypertrophy.
  • Atrophy.

Accordingly, the symptoms also differ. For example, with hypertrophic rhinitis, nasal congestion occurs, which does not go away after vasoconstrictor drops, and nasal voice. And the atrophic process is characterized by a feeling of dryness, itching and tickling in the nose, as well as crusts that form due to the accumulation of viscous mucus. But all of these forms are accompanied by difficulty in nasal breathing and a decrease in smell. In chronic rhinitis, in addition to atrophic, there will also be discharge (mucous or mucopurulent).

There are several types chronic rhinitis which have certain differences in the clinical picture.

Additional diagnostics

For more information about what a runny nose is and why it develops, provide laboratory and instrumental methods. Diagnosis of the state of the mucous membrane includes the following studies:

  1. General analysis blood and urine.
  2. Serological analysis (antibodies to infections).
  3. Nasopharyngeal swab (microscopy, culture, PCR).
  4. Allergic tests (skin, scarification, injection).
  5. Rhinofaringoscopy.

The results of these procedures are able to dispel any doubts that have arisen during the clinical examination of the patient. They also allow you to make a final diagnosis indicating the nature of the pathological process and its causes. And then the runny nose is subject to medical correction.

- this is one of the manifestations of a cold, which causes a lot of inconvenience, partially deprives the sense of smell, reduces appetite, and creates difficulty breathing during sleep.

The common cold has a second name - rhinitis (inflammatory process of the nasal mucosa). There are two types of rhinitis: acute and chronic.

Causes of a runny nose.

The most common cause of a runny nose are viral infections that cause SARS (acute respiratory viral infection). Bacteria infect the mucosa nasal cavity again, after viruses, which is the cause of complications.

Hypothermia affects the development of the disease. Less commonly, a runny nose is caused by trauma to the nasal mucosa. foreign bodies, harmful factors (smoke, dust), surgical manipulations with the nose. Viruses enter the air during inhalation, penetrate into cells that have cilia, and develop there for up to three days. Because of this, the work of cells is disrupted, the removal of foreign bodies from the mucous membrane. During normal operation of the body, cleansing is performed daily, but when an infection enters, conditions are created for accession and a bacterial infection.

Cold stages.

With a cold, there are three stages of development.

The first stage of the common cold (reflex).

It develops quite quickly due to hypothermia of the body. First, there is a narrowing, and then the expansion of blood vessels, swelling of the nasal conchas appears. The common cold is characterized by dryness, burning in the nose, shortness of breath, sneezing. Duration several hours.

The second stage of the common cold (catarrhal).

The duration of the second stage lasts up to 3 days, develops due to viruses. There is a decrease in the sense of smell, watery discharge from the nose, shortness of breath, stuffy ears, hoarseness of the voice, lacrimation. There is a clear redness of the nasal mucosa.

The third stage of the common cold.

The general condition begins to return to normal, nasal breathing and smell are restored. Discharge from the nose becomes thick, yellow-green in color. The redness of the nasal mucosa decreases, the lumen of the nasal passages increases. As a rule, the disease cycle lasts no more than 10 days, but with weakened immunity or prolonged treatment, the disease can drag on up to 3 weeks, which leads to serious complications.

Acute and chronic runny nose.

In acute rhinitis, a sharp onset is noted. The infection affects both nasal passages. There is a burning sensation and a feeling of dryness in the nose, sneezing and sore throat. Acute rhinitis may be accompanied by weakness, fever, decreased performance. Appear liquid transparent selection from the nose, which after a while become thicker and acquire a yellow-green color. Difficulty breathing, deterioration in the perception of taste, the sense of smell disappears, the nasal membrane swells. In some cases, there is noise in the ears, tingling.

Chronic rhinitis has several varieties:

hypertrophic.

It is characterized by inflammation and thickening of the nasal mucosa, leading to the closure of the lumen of the nasal passage. There is a headache, dry mouth, worsening sleep, mouth breathing.

atrophic.

With this type of runny nose, the nasal mucosa becomes thinner, mucus is secreted, crusts appear that make it difficult to breathe.

Allergic.

Manifested by watery year-round discharge from the nose. There is burning, itching, an attack of sneezing. Allergic rhinitis may cause allergic conjunctivitis.

Causes of chronic rhinitis.

Prolonged acute runny nose

Disturbance of blood flow in the nasal mucosa in diseases of the lungs, kidneys, heart, hormonal system

Irritation of the nasal mucosa by secretions of pus

Prolonged exposure to harmful factors (odors, harmful fumes, dust)

The flowering period of certain plants

Cold treatment.

At the first manifestation of symptoms acute cold it is necessary to take a hot foot bath with the addition of mustard for 10 minutes. After the bath, it is best to drink hot tea with lemon, linden or raspberry, or a decoction of blackcurrant or rosehip. Hot baths and bed rest are recommended. Wear socks with mustard sprinkled on your feet. Mustard has an irritating effect on the soles of the feet and has a temperature effect. It is recommended to take vitamin C - it stimulates the immune system, has an anti-cold effect.

For the treatment of the common cold, inhalations with aromatic oils are used - mint, lemon, tea tree, eucalyptus, lavender. At high temperature should be taken antipyretic drug. People with allergies are advised to take antihistamines.

The site provides reference information for informational purposes only. Diagnosis and treatment of diseases should be carried out under the supervision of a specialist. All drugs have contraindications. Expert advice is required!

Runny nose is an inflammatory process covering the nasal mucosa. This disease most often accompanies other ailments. This is usually a sign of another disease. Rhinitis- this is common occurrence with acute respiratory viral diseases, such as parainfluenza, flu , measles , adenovirus... With such combinations, doctors call a runny nose rhinitis, which in Greek means " nasal inflammation".
Patients prefer to call this disease a runny nose. The first and second names, although they are very similar and even synonymous with each other, are nevertheless somewhat different. Yes, the name rhinitis” implies the mechanism for the appearance of the symptom, then the name “ runny nose"speaks of signs of inflammation, for example, the expiration of mucus. In this material, there will be no particular distinction between these two terms.

AT in large numbers cases of rhinitis allergic manifestation and develops when a provoking agent enters the tissue. So, there are two types of rhinitis: allergic and infectious. You can read about why and how these two types of disease occur in this article. It must be said that a minimum of information about how rhinitis develops will help people who do not have medical education, not only competently approach the treatment of this disease, but also prevent its occurrence.

What are the causes of rhinitis?

For any reason, causing the appearance rhinitis, this is necessarily a sign of an inflammatory process on the nasal mucosa. Allergic and infectious types of diseases differ from each other not by the mechanism of occurrence, but only by the cause that caused them. There are some specific factors in the structure of the respiratory system that contribute to the development of this inflammatory process. Following are some of them:

1. The nose is the most important place through which atmospheric air enters the body. For human health, it is necessary that breathing is carried out through the nose. Eastern sages had a saying that inhaling air through the mouth is the same as eating food through the nose.

2. The nasal mucosa is constantly “tested for strength” by a variety of aggressive factors, such as pathogenic microflora, icy air, aggressive substances, dust, pollen and other allergens. Thus, it is here that all these agents are rendered harmless. Dust particles settle here, the air acquires the necessary temperature and humidity for entry into the bronchi and lungs. Due to the abundance of small capillaries in the nasal mucosa, a runny nose develops. This mechanism will be discussed in more detail below.

So, the nasal mucosa is constantly under the influence of quite aggressive factors. Therefore, a runny nose is a fairly common occurrence.

Infectious runny nose

Infectious rhinitis ranks first among the signs of infectious diseases that affect the upper respiratory organs. In addition to rhinitis, with such diseases, there are necessarily a number of symptoms characteristic of infectious diseases. Often, along with rhinitis, migraine-like pain is observed, body temperature increases, and lethargy develops. Runny nose in this case is caused by the action of pathogens on the nasal mucosa. As it was said, this organ is the “first front line” in protecting the body from a variety of damaging factors. In this regard, a huge number of microorganisms constantly enter here. The vast majority of these microorganisms cannot cause disease, but there are some that can be the cause of the development of the disease. In the case of an infectious rhinitis, an increase in the number of harmful microbes on the nasal mucosa causes a violation of its condition and the death of the upper cells. This phenomenon is the explanation for the symptoms of rhinitis: itching in the nose, the appearance of mucus from the nose, "clogging" of the nose, a violation of the timbre of the voice, and much more.

It must be said that the appearance of mucus from the nose is the response of the blood vessels of the mucosa to the inflammatory process. The appearance of mucus is an attempt by the body to evacuate harmful agents from the nose. It must be said that by appearance and the amount of mucus can be judged by which microorganisms the process was provoked. In the case when the mucus is transparent and liquid, most often this is a viral origin of the disease, but if the mucus is yellow, then the cause of the disease is bacteria.
Speaking about the infectious form of the disease, it must be said that this is often the first sign colds. In this connection, at the first symptoms of rhinitis, treatment should be started immediately. Then the process can be stopped in time.

allergic rhinitis

The main signs of an allergic form of the disease are the same outflow of mucus and "clogging" of the nose. The process of development of this disease is completely different from that of the infectious form. The impetus for the onset of an allergic rhinitis is the interaction of the nasal cavity and any allergen. Together with microorganisms, a huge number of these substances enter the nose: this is the hair of cats and dogs, and pollen, and household dust, and much more. If the human body is prone to allergies, then such contacts provoke a violent reaction. In the place where there was contact, the inflammatory process begins. The appearance of an abundance of mucus in this case indicates the "desire" of the body to quickly wash out all allergens from the nasal cavity. Often, this form of rhinitis is accompanied by inflammation of the mucous membrane of the eyes, lacrimation, and respiratory failure. It is these factors that indicate the allergic origin of the disease. Suspicion of this form of rhinitis is a reason to visit an allergist's consultation.

A related disease is neurovegetative rhinitis. Both varieties belong to the vasomotor group. In this disease, the symptoms appear due to the instability of the nervous regulation of the state of the blood arteries.

A runny nose is a phenomenon familiar to everyone, and almost everyone believes that he has enough knowledge and experience to be cured. However, most people make mistakes when trying to get rid of rhinitis and share many misconceptions about it.

Consider the most common of the myths about this disease.

Source: depositphotos.com

Runny nose - a slight malaise, not dangerous for the body

Rhinitis, as a rule, is not an independent disease: more often it is only a symptom characteristic of many pathologies. It can be allergic, bacterial, viral in nature. In any case, a person suffers from nasal congestion, shortness of breath and a feeling of fatigue, sleep is disturbed, and appetite decreases. All this is unpleasant, but not too dangerous.

Real problems begin if the patient treats the treatment of the common cold without due seriousness. In the absence of treatment, complications such as sinusitis and sinusitis often develop. At further dissemination The inflammatory process can affect not only Airways, but also the organs of hearing and even the meninges, which is really life-threatening.

Runny nose due to hypothermia

A common misconception is that if you get your feet wet, you'll catch a cold. In fact, the development of rhinitis is not directly related to hypothermia. The common cold, a symptom of which is a runny nose, is viral in nature, and susceptibility to pathogenic microorganisms depends on immune system. Therefore, a small draft is enough for one to “snuffle”, while the other remains healthy even in a severe frost.

Infection occurs by airborne droplets, so a person with a weakened immune system during seasonal colds should avoid crowded places (shopping centers, crowded public transport, etc.).

With a cold, you need to take immunomodulators

If a runny nose has broken out, taking drugs that activate the body's defenses is not only useless, but also dangerous - because the increased secretion of mucus from the nose is in itself a consequence of the immune system's reaction to pathogenic microflora. By artificially boosting this process, you can aggravate the problem and get a serious immune disorder instead of a cold. Fortunately, most immunomodulators are drugs with unproven (that is, not detectable in any way) effect.

Green discharge from the nose is a sign of a bacterial infection

This is not always true. Thick green mucus discharged from the nose with rhinitis is a sign successful work immune system. As the disease develops, the color and consistency of the secretions change: at the beginning of the disease, they are transparent and liquid, then they become white-yellow or greenish and thicken. This is due to an increase in the number of white blood cells that fight pathogens.

To make a runny nose go faster, you need to blow your nose often.

With a coryza, the nose seems to be filled with secretions, and the patient strives to bring them out to facilitate breathing. But unpleasant feeling is not associated with an excess of fluid (mucus), but with a strong swelling of the mucous membrane. Attempts to blow your nose sharply and strongly are unsafe: in this case, part of the mucus is pushed deep into the sinuses and even into the auditory canals, infecting them and thereby provoking the development of sinusitis, sinusitis and otitis media. It is necessary to clear the nose of secretions very carefully, avoiding sharp pushing movements, each nostril separately.

All cold drops are safe

Especially enduring myths are associated with drugs for the common cold. Most people, having felt nasal congestion, immediately begin to use vasoconstrictor drops. They do give temporary relief, but with frequent use they are addictive.

Drops should be injected into the nose, slightly tilting the head back and turning it towards the nostril into which the drug enters. It is not necessary to bury the medicine while lying on your back - otherwise the solution does not linger in the nasal cavity, but immediately flows down the throat.

Vasoconstrictor drugs should not be used for longer than three days. More secure funds plant-based containing oils (for example, "Pinosol"), as well as solutions for washing the nose based on sea water (for example, "Aqua Maris").

Runny nose can be cured by warming the nose

Folk medicine recommends two types of heat exposure to help cure rhinitis: dry warming (for example, using a linen bag with heated salt or sand attached to the bridge of the nose) and hot steam inhalations.

Dry warming is useful only at the very beginning of the disease, while the discharge from the nose has a watery consistency. A hot dry compress helps to reduce swelling of the mucous membranes and thereby facilitate breathing. If the runny nose has moved to the next stage, it is impossible to apply heating, otherwise the vital activity of pathogens is even more activated.

Inhalations with a runny nose are dangerous by creating a warm and humid environment in which bacteria feel especially comfortable. In addition, inhalation of hot steam is fraught with increased mucosal edema and even burns.

Attention! Any thermal procedures are contraindicated in case of elevated temperature in a patient and a serious deterioration in the general condition.

It is useful to instill garlic or onion juice into the nose.

Quite a cruel and ineffective procedure. With a runny nose, the nasal mucosa is already irritated, and the caustic juice injures it even more.

It is much more reasonable to gradually introduce these vegetables into the patient's diet, and also place them cut in his room so that the released phytoncides disinfect the air.