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Home > Dr JB Lim's Corner > Nose bleeding and effect of dry cabin air.
Nose bleeding and effect of dry cabin air.
Flying - Dr JB Lim's Corner
Thursday, 06 December 2007 18:50

Dear Captain Lim,

Many thanks for your e-mail to keep me updated on the latest about flying and all those jets you are enjoying. One enquiry by one of your visitors called Sani (Q 7 Collection 30, November 7, 2004) about nose bleed and dry air struck me, and I thought I should also give my view point. I hope you allow me to comment as your website is very dynamic and interactive, and can serve as a forum exchange. The question Mr. Sani asked is an area in medicine that interest me a lot as a physician, and as a Trainer for St John Ambulance Malaysia. It is also my involvement in Emergency Trauma Care, and also as a Scientific Adviser and Editor for the Malaysian Society for Grammatology and Emergency Medicine, besides being also a Life Fellow of The Royal Society of Medicine (RSM) in London, with special membership in the Accident and Emergency Section of the RSM.

Nose bleed or epitasis is within the scope of emergency medicine which we may have to deal with, especially in trauma cases of the face and maxilla-facial region. So kindly allow me to interact with an opinion.

The most common causes of nosebleeds are:

1. Trauma or a blow to the nose
2. Fragile blood vessels
3. Disturbing the crust formed in the mucous membrane as a result of common cold or an infection.

Rarely is epitasis caused by:

Dry nose due to low humidity. I am aware that some questionable Internet sources pinpoint that as prime cause. This is entire not true at all. There are also other causes of course, albeit rarer. These are :

Vitamin K deficiency. This rarely occurs in adults as most of the vitamin K is synthesized by the bacteria in the gut. In neonates and new born babies, this may be the cause of any bleeding, not just nose bleeds, as the gut is still quite sterile, and has not acquired sufficient vitamin K through bacteria gut synthesis.
However it may occur in adults on antibiotics therapy, as this may wipe off all the bacteria in the intestines responsible for synthesis of this blood-clotting vitamin. This may cause bleeding through the nose as well as any part or orifices of the body.

Genetic disorders such as hemophilia, inherited connective tissues disorder Ehlers-Dandles syndrome may also cause the nose to bleed. There are congenital hematological (blood) disorders that include hypoprothrombinemia, and an acquired version called dysprothrombinemia. All these can cause epitasis due to some defect or deficiency in some of the clotting factors.

I have personally treated a numbers of patients with frequent epitasis caused by ITP (Idiopathic Thrombocytopenic Purport). The cause of ITP is not known, hence the term “idiopathic” which means “unknown” or “spontaneous in origin” It has been shown that that people with ITP produces antibodies that destroy their blood platelets in the spleen. ITP is thus an auto-immune disorder that can also cause the nose to bleed. The spleen produces the antibodies that destroy the blood platelets, and at the same time it also destroys old or damaged blood cells. Hence the spleen becomes enlarged (splenomegaly) due to excessive destruction of these blood corpuscles and thrombocytes there. In people with ITP, however, the antibodies attack the body's own blood platelets causing the thrombocytes (platelets) count to drop. This results in bleeding under the skin (purport), and gums The nose bleeds easily as well. The thrombocytes is responsible for normal blood clotting.

Sometimes ITP or a low thrombocyte count due to other causes is characterized by tiny red dots on the skin (medically known as petechiae) or inside the nose as Mr Sani described. Bleeding disorders including epistaxis (nose bleeds) may also be caused by low platelet count due to various causes. So is hypertension, and tumor of the nose or of the Para nasal sinuses. Physicians normally would also look at all these possibilities, and underlying causes in patients whose nose bleed easily and frequently, as these are not caused by dry air. Low humidity although quoted by some sources is not the prime cause. If that was the case, all inhabitants living in very cold regions of the world, and where humidity is very low will experience frequent nose bleeds? So would the majority of all air passengers and cabin crews flying about in an air plane. But is there any statistics show this?

In fact the blood vessels lining the nose are so fragile and sensitive since they are located near the surface. They may swell up and burst easily by a decrease in the atmospheric pressure, just as the ear-drums seem like bursting with increasing or decreasing latitudes. We can demonstrate this by applying a suction tube over any thinner part of the skin. We can immediately see blanching and reddening over that area where the section tube is applied. The lower air pressure in the ‘vacuum’ tube attempts to bulge to suck out blood from the underlying capillaries. This causes redness. But it cannot cause bleeding since the elastic skin protects the blood vessels below. But not in the thin and un-protective mucous membranes that lines the nose. The vessels there just bursts at the slightest trauma, a blow on the nose, and possibly even in slight difference in air pressures. I know the cabin pressure is equalized, but on countless occasions when I flew, my ear-drums almost felt like bursting. Even the tougher ear drums felt almost like bursting, what about the much more tiny, and more fragile blood vessels that line inside the nose?

In our Malaysian experience, a considerable number of patients with epistaxis have been treated in emergency departments of hospitals. The cause(s) of epistaxis in our hospitals has nothing to do with humidity. Malaysia is a very humid country with humidity hovering around 85 – 95 % in the tropics, and yet we have lots of patients coming in with this problem, especially among children. Sometimes it was the result of a common cold or some upper respiratory tract infection. But most of the time, the nasal blood vessels are very fragile, and they tend to bleed at the slightest knock or a scratch into the nostrils.  In fact medical history taken from patients with nose bleeds showed that those working for long hours in cold storage rooms in food processing factories, as well as in air-conditioned rooms where the humidity are much lower than outside, the incidence of nose bleed is not in anyway higher than those working outside in the streets where the environment is really hot and humid.

As far as my knowledge is concerned, there is no statistically difference between relative humidity and incidence of epistaxis, even though some sources claimed (without a proper evidenced-based study) that low humidity causes epistaxis. Many text-books of medicine don’t even mention humidity as one of the aetiologies (causes). It is completely not there at all. They gave trauma, digging the nose, blood disorders, etc as the prime causes. In fact if the air is very dry, the outer skin which is dead and horny, tend to crack and bleed a little. This is experienced in chapped lips, cracked soles of feet, and hands, and where there is little sweat pores and sebaceous (oil) glands. In very cold environment, this problem is made worse because all the peripheral blood circulation beneath the skin are shut down in any attempt by the body to drive the warmer blood to the deeper parts of the body to conserve body heat.

This includes the sweat and oil glands as well as the peripheral circulation which almost all shut down. That’s why we don’t sweat in cold weather. This is because the skin is not so important, compared to the vital organs of the body. Thus the outer skin can afford to crack and bleed slightly, and becomes a little itchy. This will not affect the other vital functions of the body. The body is very wonderfully made. It can differentiate and prioritize which function or areas of the body are more important, and divert its attention there.

For instance, it will shut down the less important ones, such as skin circulation in order to drive more blood to other vital parts of the body. In doing so, it converse more body heat so that the more blood can flow to the vital organs such as the heart and brain to avoid hypothermia and unconsciousness. Then there are areas of the body such as the nasal opening – the first part of the airways and the lungs which must be kept moist all the time to facilitate the exchange of gases (oxygen, carbon dioxide, including the expulsion of water vapor from the lungs). These areas cannot afford to dry up at all just a because of the low humidity.  The same with the digestive system where nutrients need to be absorbed through the gut via a moist intestines. Technically these systems are outside the body where air can reach them. Imagine they all dry up because they are exposed to the dry air ? They just cannot afford to do so. If they do, the system will fail. In order to do so, these areas are lined with thin mucous membranes (unlike the dead and thick skin) which are kept moist all the time by biological fluids and secretions, such as mucus, and mucin produced by mucus glands. The sinuses in the nasal cavity contribute towards this role.

Sometimes because of an infection or an allergic reaction, the sinuses over do this with secretions, and they make the nose run badly – called post-nasal drips or catarrh. When the air gets too dry over these areas, such as in the nose (part of the airways), the mucous glands will immediately compensate via a feedback mechanism by secreting more fluid and mucous to keep the lining damp and moist. But if the environment (stimulus) such as very dry air is prolonged as when staying in the desert or through prolonged exposure in winter when the air is both dry and cold, some of these compensatory feedback mechanism may no longer function properly due to persistent stimulation (sensory fatigue). In such cases, the skin becomes a little more horny, dry and a little bit more rough, In the case of the mucous membrane, may be a little less effective, and seems to adapt with lesser secretions. But still it will not shut down completely.

However in some individuals, this compensatory mechanism to produce more mucous and nasal drips under adverse conditions (stimulus such as very dry air), or as an allergic response to dust, smoke and pollens, it may no longer is operative. In such individuals, dry air may cause the upper respiratory tract to dry up a little until the nasal lining crack and bleed.

Sometimes they become red and inflamed but I have not much experience studying this possibility as we all live in a hot, humid tropic country, and we don’t see this problem at all. Instead, despite the high moisture content in the air in Malaysia, our patients still bleed from the nose as seen in out-patients departments of hospitals nation-wide, and in pre-hospital care attended by our paramedics and ambulance crew. Obviously this has nothing to do with humidity. Because of this compensatory mechanism, people who are not used to cold and dry weather will find their nose wet and running when they get outside into the streets in dry and cold winter months. But their nose generally doesn’t bleed.

This “running nose” has nothing to do with the common cold which is caused by rhinovirus. In a common cold we sneeze and have running nose. We can see the rational why our body does this in an infection. The sneezing and the nasal drips is an attempt by the body to get rid of as much viral load as possible inside the nasal cavity. We can see how wonderfully this body of ours is designed, so why stop the nasal discharge with antihistamines, and antibiotics which has no effect at all on viral infection. But the case of very dry air, not only our noses will run, but even our eyes become watery (hyper-lacrimation) and irritated due to overcompensation by the tear glands to secrete more tears to prevent the eyes from drying up. Everyone who has not experienced very cold winters when the humidity is very low will get this sensation.

My nose always ran whenever I got outside the university and hostel buildings during the winter months when I was studying in London. My eyes would be wet and red. But the moment I step back inside the warmer building, that “running nose” and “crying” seems to stop almost at once. This was just a physiological response, and it was not a disease or an infection. This is something every doctor “ought” to know (some don’t), and “ought” to be able to explain to their “patients” All well-trained and qualified physiologists know this physiological response. Again some very specialized physiologists with PhDs degrees don’t. This is because they have forgotten all the basics taught to them in their earlier Bachelor’s class. They forgot all these ABC functions of body once they get too specialized, too deep, too isolated in their knowledge and their area of specialty.

So generally in areas of the body where there are secretions by the mucus membranes they don’t crack or dry up easily unlike the lips or on their hands. When these glands over secrete over long exposure to overcompensate, they may undergo atrophy (wasted and break down), and they may become less effective. That’s why inhabitants who live permanently in cold and arid regions of the world, they may not experience “running nose” or excessive acclimation, or even epistaxis unlike an un-adapted new comer would. But those who are not used to very dry air, their hands, and feet, and lips (physiologically much less important areas) may dry up, crack, bleed, become sore and itch a little. Occasionally one may find his nose bleeding if the nose does not drip a little. But over longer periods of adaptation, even the linings of the nose becomes thick a bit, and there will be less “running nose” But I am unsure if this will lead to epistaxis as some sources claimed. I am aware of these claims, but they cannot produce evidence-based statistics. It is not in the reference medical text-books anyway.

As I said, the external skin is relatively less important unlike the vital systems of airways and the respiratory system. Especially the lungs where there is very vital exchanges of gases going on all the time. Imagine the lungs get dried up because of the very low humidity ? The result is almost instant death due to ventilatory and tissue respiratory failure. Even though the nose is less important being not involved in gas exchange, it is the first part of the airways. Still it has a function to trap dust, dirt, smoke particles and reasonable-sized foreign bodies in the air before it reaches the lungs. It can only do this job through the hairs in the nose that act like coarse filters, and also by making the nasal cavity moist and sticky (like gum) with mucous secretions.

However, I am also unsure in practice if the incidence of epitaxis among tens of millions of air passengers who fly everyday all over the world, is any higher (due to low humidity in the cabins) than those who don’t fly at all, or stay in humid climate. Is there any reliable large-scale medical statistics from proper study to show this ? Unless a well-designed, randomized, large-population and statistically-planned study, with controlled groups is conducted to show the correlation between the humidity in the air and the incidence or episodes of epitaxis, we cannot justify that the prime cause of epitaxis is due to dry air. In the Internet, some popular books and health magazines may claim all that. They even show colored pictures. What we need is scientific evidence-based statistical data, not some pictures. To the best of my knowledge, no study has been published on this. The mucus in the nose or elsewhere don’t just dry up, crack and bleed like that, no matter what some old edition medical text-books may write, or Internet may claimed. If this was so, all the millions, and millions of air passengers, including the cabin crew and the pilots who fly everyday will get their nose bleeding the moment they enter an aircraft. Some of these medical text-books including Internet claims are fit for a bonfire when medical advances and understanding are so rapid through research these days.

Unfortunately, these information are available only in technical journals which most people, including practicing clinicians and doctors don’t read, or bother to read. Even if they attempt to read, they still don’t understand what was written inside, because the paper was written in a very highly elegant technical language by the researchers. So they avoid reading it. . They feel more comfortable just treating coughs and colds, and listen to drug salesmen sales talks. They don’t even attend Continuing Medical Education (CME) sessions by their research-oriented colleagues to gain credit marks. In summary, it is unfortunate Mr Sani did not disclose his age. That would have helped a lot in the diagnosis. In small children this is a very common problem which rectifies itself as the child grows up. But for elderly individuals to experience sudden off and on epistaxis whatever the humidity, this underscores a much more serious underlying problem that needs to be thoroughly investigated. Nose bleeds in adults and elderly people maybe due to a cancer, a neoplastic disease, or some underling blood disorders. A medical history, and age of the patient are some of the vital diagnostic clues, besides a physical or a radiological examination
In their absence, it is very hard to make any inference. Maybe it is just a simple problem that can be resolved by frequently spraying saline or even plain water into each nostril through a nasal spray canister whenever the affect victim travels by air. More lasting effect is to rub into each nostrils some petroleum jelly. That should do the job if we can definitely conclude that very dry air was his problem.

Part Two

The other comment I need to make is when you mentioned to Mr. Sani “Eat foods that are low in salt and sugar because this helps your body to retain moisture” I think this is the opposite from what we know. High salt (Sodium chloride), and not low salt intake actually retains water in the body (water retention). This is very easy to understand. Accumulation of water (fluid retention) actually increases the hydrostatic pressure in the blood and blood fluid. Sodium remains in the intercellular spaces of tissues – but outside the cells Any increase in hydrostatic pressure will naturally elevates the blood pressure due to this fluid (water) retention.

A low sodium, but high potassium intake does the opposite. Potassium remains inside the cells, while sodium is outside the cells in the intercellular fluid. Low salt intake throws out excessive water from the body, and thus lower blood pressure. The physiological rationale behind is very simple. Consider this very simple analogy. You keep pumping air (like water) into a car tire to inflate it, don’t you think the internal pressure (like blood pressure inside the vessels) in the tire (like body) continues to rise until it burst (like having a hemorrhagic stroke). Hemorrhagic stroke is the bursting of one of the cerebral blood vessels in the brain. In fact any blood vessels like those in the nose can also burst due to hypertension.

The blood maintains a certain level of (is) tonicity or normal physiological osmotic pressure with a correct balance of salts (electrolytes) sugars, proteins, and of course water in the blood. If this delicate biochemical-physiological balance is upset, such as taking a lot of salt in the diet, the body will try to balance it out by making you feel thirsty. The result is that you will have to drink a lot of water in order to dilute the excessive salt inside. This is merely an attempt by the body to lower the increased osmotic pressure due to high sugar and salt in the blood. It will try to bring it back to normal osmotic pressure (isotonic) by increasing water intake through its thirst mechanism. That extra intake of fluid is to dilute the salt and sugars so that in can reestablish the normal isotonic pressure. But a normal osmotic pressure made good by drinking a lot of water because of thirst, causes a rise in the hydrostatic pressure within the tissues, including the intimae (inner coat) of the blood vessels. This is where blood pressure is maintained.

That is why if you have mild high blood pressure, your doctor wills advice you to lower the salt intake in your diet - so as to lower water retention. This is the first line of management for those with higher blood pressure. If that fails, as some patients are salt-sensitive, and some are not, he will then prescribe a diurectic (drugs that increases the flow of urine). And the first drug of choice is Potassium chloride (before he prescribes thiazides) that throws out the excessive Sodium chloride (common salt). When the sodium gets out, the water will also follow to establish the same salt-water dilution. The loss of water wills immediate deflates the hydrostatic (blood) pressure. This will also establish the normal sodium / potassium ratio (one of the electrolyte ratios) once again. This is like getting air (water) out from an over inflated tyre to normalize it. So you can see the physiological rationale behind this wonderful feedback mechanism implanted in the body to help us survive and remain healthy.

Hence your statement “Eat foods that are low in salt and sugar because this helps your body to retain moisture” needed to be corrected This is just the opposite of medical / physiological and nutritional principles. I take the term “moisture” to mean “water retention”? But anyway it was a good try from a pilot, since your advice to cut down on salt and sugar intake is almost universally recognized and accepted by the medical community to prevent heart and blood vessel diseases.

Professionally, I would advice this same thing myself together with drinking a lot of water as you have said. Drinking a lot of water does not result in water retention or increase in hydrostatic / blood pressure as the excessive water is not retained, but passed out into the urine almost immediate it is absorbed. It is the excessive salt that causes the water to be retained, and causes an increase in the blood pressure.
However recent papers published refuted this old belief that excessive salt intake causes the development of cardiovascular events later on in life. The paper says that those who are not “salt-sensitive” are not affected, compared to those who are “salt sensitive” Non-salt sensitive population have never been shown to develop hypertension throughout their lives even though their salt intake has been excessively, and constantly high. This is a very recent debate among members of the medical and nutritional fraternity.

So you can see how confusing this scientific debate is. How are we going to advise our patients when medical researchers themselves cannot make up their mind ? Clinicians only follow the researchers advice, and they in turn advice their patients. Unfortunately, I am both – a physician and a medical researcher, and I too cannot make up my mind with these findings the researchers announced. Ultimately it is the researchers – the frontiers of new knowledge and information who must make up their minds, not the practicing doctors who merely follows the learned researchers advice, and merely pass them on to their patients. So unless I read up other papers in the journals, and get a consensus of learned opinions from my counter-parts, I can only smile to my patients when they pose this question to me. Good luck to them.

Anyway, good health advice Captain, even though you are a pilot, while I am not an expert in the aviation area. So I cannot give them any advice on flying either.


JB Lim


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The ambient humidity should be approximately 50% for mite reproduction. 25-40% humidity is the ratio of ambient air is recommended for for the prevention of mite reproduction especially in person with house mite allergy. Ambient humidity of 40% 's must be on for treatment of dry nose but this is not suitable fo mite alllergy (Source: http://www.saglikhaber.info/Bu...avisi.html).

Greetings …
Very comprehensive overview. Well done on the the fact that you recognize Ehlers Danlos Syndrome being a possible cause, Its a condition many medical professionals are familiar with. As an EDS sufferer and ex-cabin crew member I appreciate the thorough accurate nature of the article. Regards, Lorraine
Lorraine O Sullivan , 11 Jan, 2014
Thank you for this article. One has to be cautious about all the articles that float around. I have a question to ask: I am 55 years old , in Bangalore, India, and had two episodes of severe bleeding nose in the last two days. Have consulted an ENT and he thinks it's a membrane rupture. I had an auto immune problem 3 years ago. Do you think I should connect this bleeding episode with that disorder of some years ago?
Meenakshi Shivram , 20 Apr, 2016

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