Allergies Explained - go back to home page Allergies

Grass pollen discharging granules on exposure to water - picture by Dr H Morrow Brown

Dust Mite - picture by Dr H Morrow Brown

Dr H Morrow Brown MD
General Medical Council Registered Specialist
for Allergy and Respiratory Medicine


Allergy to Animals

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Cats as a cause of Asthma

Allergy to pets can be a very difficult problem, especially cats. This is because the particles of dried saliva from licking themselves and their skin scales are so light that they remain floating in the air for a very long time. Cats are now so common that schools, public buildings, cinemas, buses and trains, and the clothes and even the hair of cat owners, all contain enough cat allergen to set off a very sensitive asthmatic. So even if you do not own a cat or have taken advice to find it a good home there is still some cat allergen floating in the air in most places.

An example is the patient who was very allergic to cats who was considering buying a house. He finally purchased after being assured by the previous owners that although they had a dog they had never had a cat. On taking up residence he was repeatedly admitted to hospital with asthma. Skin test for dog was negative but cat was very positive. All became clear when he found out that the cat next door used to come in every night and curl up in front of the fire with their dog, but of course strictly speaking the cat did not actually live there!! He had to re-decorate that house from top to bottom before the effects of the cat were eliminated. Recent research has found that some infants who are raised with cats may become immune to them, while others become very allergic, so there is some controversy regarding the best policy.

Another patient found that every time he spent the evening in his local pub he had a very bad night with asthma, so he was advised to stop drinking beer as the being the most likely cause. He had no problem while drinking vodka for some months in different pubs, but when he went back to his local some time later he found that beer had no effect. What he had not told me was that in the meantime the owners of the pub had gone bankrupt, and the new owners cleared out the cats which had infested the place, and sat on the window sill watching him drinking his beer!

Tiger skin rugFor some years patients waiting to see me sat on a sofa covered with a very old tiger skin. One day I noticed that a little boy who was cat allergic, and had been much better since their cats had been found a good home, was sniffling and wheezing by the time he came in to see me.

Recalling that tigers are just the big cats, I made an extract of some Tiger hair for testing with the result shown.

From the allergy point of view there does not seem to be much difference between various breeds of cat, so I made a testing extract from the hair of a Siamese cat and compared the skin test reactions on the owner of the cat, which seems to confirm that there is not much difference between breeds of cat. Test extracts I made from long and a short haired cats showed that the long haired cat was much more allergenic than the short haired, as I expected.


Dogs as a cause of Asthma

Dogs are not such a problem to the allergic person, as they do not seem to contaminate the environment so much. Allergy to the Mexican hairless dog has been reported, but I have never seen this. One unique patient is definitely very allergic to dogs, but not to the bitches which she has kept for many years in very close contact.

Dogs can also cause other allergic problems, such as eczema. Because the possibility is very seldom considered dogs are unlikely to be diagnosed as the cause of eczema, so the true frequency of dog eczema is completely unknown. The clue is often that a holiday in the sun, which helps most cases of eczema anyway, brings notable improvement in the child’s eczema, and the longer the holiday the better. On return home the eczema flares up overnight, because of environmental allergens.

The boy with eczema illustrated above had improved on a milk free diet, and then cleared completely on holiday in Spain. On the way home from the airport in the car for one hour with the dog which had just been collected from kennels, this boy began to scratch himself to pieces, and three days later he was as shown. After removal of the dog and a house-cleaning, and continuing the milk free diet, his eczema completely cleared. The lesson is that there are often several causes of eczema, and that the possible effects of environmental allergens should never be overlooked.

In my experience to find the dog a new home or put it outside in a kennel is more effective than finding a home for a cat. Ignorance of the possible effects of a resident dog can give rise to gross injustice. For example, Sandra was aged 12 when she was finally seen at the clinic with a referral letter stating that she had chronic asthma with a major emotional factor because her father was frequently in trouble with the law and often in jail.

She just sat there very withdrawn, hunched up, and completely inactive, her appearance suggesting that there was indeed an emotional problem. Her best peak flow was only 50 litres/min, a very low figure indeed, so she did not have enough breath to do more than sit still !! The peak flow record above shows how wrong that diagnosis was, because after rescue with a course of oral steroids she was not properly controlled with Becotide until the dog was put outside in a kennel. Some months later she stopped all medication and remained free from asthma.

When a pet is proved or suspected to be the cause of asthma in a child the parents often have difficulty in accepting that their beloved pet is the cause, and that removal is the only sensible answer as desensitisation is not possible in this country. We are such a nation of dog lovers that these priorities may not be acceptable, so that expensive drugs are often being prescribed to suppress the effect of the continued presence of the animal. This policy may not be pursued vigorously because many doctors are fond of dogs and have dogs themselves, or they are unaware or do not accept the importance of allergy to pets.A recent survey showed that in this country advice to find a pet a good home is not usually pursued vigorously.

The most important evidence indicating the pet is the cause of the problem, whether it be rhinitis, asthma, or eczema, is recovery on holiday followed by swift relapse on return home. This scenario is also typical of dust mite allergy, so skin tests and monitoring the effects of being away from home in a dog free environment on the peak flow may be necessary to confirm that the dog is the culprit.

This is an example of a case where the boy’s mother could not accept that her beloved pet could be the cause of her son’s asthma, which was so severe and chronic that he had a severe pigeon chest deformity as a result.

The peak flow chart illustrates how he recovered with high dosage steroids in hospital, relapsed promptly
on return to his dog contaminated home, and stabilised on the removal; of the dog and its traces.

Horses are another cause of allergy, particularly asthma, which can also have emotional aspects. When I discovered that a little boy’s life-threatening asthma attacks were caused by his elder sister carrying horse dander into the house on her riding clothes she was so incensed that she wished him dead!

The use of horse hair as stuffing in antique furniture is also an unusual cause., as in the teenager who began sneezing and wheezing when he lay on his stomach on an antique sofa looking at TV, and had asthma every night because he was sleeping on a mattress which was 40 years old and full of mites. Renewal of the mattress and avoidance of the sofa were remarkably effective.

Grooming horses produces a surprising amount of horse dander which triggers off the asthma or rhinitis. Horses eat hay, and if the owners are pollen sensitive they may get hay fever when handling hay which was pollinating when it was harvested, but can tolerate ‘seeds’ hay which has already pollinated.

The environment of the stable harbours other potential causes of trouble for the allergic horse owner, because if hay is mouldy it can also cause not only serious asthma and allergy, but also farmer’s lung, which can be really serious for both rider and horse. They should always be asked if exposure to mouldy hay is followed by influenza-like symptoms suggestive of farmers lung.. The bedding of the horse is also a potential source of trouble, but this can be dealt with by substituting synthetic material which is now available. Horses can get allergies too!

A chronic asthmatic patient had a horse which was shown by a RAST test to be very allergic to three species of mite, grass pollen, and all cereals. This finding created great problems!.

Any pet can cause a problem, and a special testing solution may not be available. A good example is the lady who developed rhinitis with very severe sneezing attacks. Her little boy had been given a chinchilla for his birthday some time before she developed her problem, and she got better on holiday. The chinchilla is a rodent from South America which can be used to make very expensive fur coats.

Because skin tests for dust mite and all common allergens were negative she was asked to come back with a sample of the animal’s hair, and also some house dust collected from the top of the wardrobe. She brought only a few wisps of hair, but this was enough to make an extract in a syringe which produced an immediate skin reaction, and so did an extract of the dust from the top of the wardrobe., as shown, but the usual dust mite test was negative. Fortunately she was soon to move house, so it was advised that the chinchilla be kept outside after they moved to the new house, and there was no further trouble with allergic rhinitis.

Any exotic pet can cause allergy problems in allergic people, the strangest in my experience being a Kinkajou. For many years nobody suspected, especially the skin clinic, that this was the cause of this teenager’s chronic eczema. He had generalised eczema as well, worst on the hands which touched the animal. When the animal died the eczema cleared up completely!.
Chronic Eczema of hands before Kinkajou Died Hands a month after Kinkajou died


Dog Story

Yvonne was 37, worked at the hospital and had been plagued with eczema for 14 years which mainly affected her face. She was using antihistamine to suppress itching in bed, and steroid creams. She had become anxious about long-term effects on her skin, but the dermatology department had no further suggestions.. She had had a dog for 18 years, and the eczema improved when on holiday in Europe. Skin test for dog was +++, and RAST was ++++, but she was very anxious not to have to get rid of the dog as she was so fond of it.

At the time some research was being carried out with tannic acid, which has the property of binding and coagulating proteins such as dog dander. She was supplied with tannic acid to make up and use as a spray everywhere in the house, and the eczema disappeared completely for over two months. At that point she found that on return from holiday the effect of the dog became evident again, but with further use of the tannic acid the eczema again subsided. Tannic acid was fairly easy to obtain, but strong tea is a good substitute.


"It is a paradox that while Britain has the highest incidence of allergic disease in the world, it also has the most inadequate allergy service"

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