Environmental Allergens

Filed under: 4 - Atopic Dermatitis

The environmental allergens which most frequently cause atopic derma­titis are house dust, pollen, and wool. In addition to these I have seen it caused by horse and cat dander, cot­tonseed, Kapok, and feathers. It is probable that these allergens, with the exception of wool, work by in­halation more than they do by con­tact.

For young infants, house dust and wool are the most important of the environmental allergens. Pollen as a cause of atopic dermatitis is unusual in infants-the youngest child that I have seen, in whom I was sure it was a cause, was 2 years old. If my figures for intracutaneous skin tests with dust and feathers mean anything, and I am not entirely sure that they do, these two allergens are frequent causes of atopic dermatitis in infants; this is, however, pretty hard to prove. As a routine treatment it is well to remove feathers from the environ­ment, and dust and wool in so far as it can be done. What one sees so often is a highly allergic baby with atopic dermatitis in whom it is diffi­cult to prove any specific clinical sensitivity except for egg white.

It is in children after the age of 2 years that the environmental allergens are most important, and if the eczema began late, that is, after the age of 10 or 12 months, and particularly if it began back of the knees and in front of the elbows instead of on the face, the chances are that it is due to environmental allergens. I am sure that many children after the age of 2 years have atopic dermatitis from house dust.

In children who have had atopic dermatitis for several years, a history of seasonal exacerbation is of the ut­most importance. Many of these chil­dren are worse in the winter and their eczema begins each fall, “as soon as the heat is turned on.” It lasts all winter, reaches its height in March or April, and then begins to subside, so that during the months of June, July, and August there is little or no eczema. Such eczema is often due to wool or to house dust or to both.

Another group of patients is nearly free from eczema in the winter, and has it especially during the pollen season, with or without hay fever. These patients are common, and it seems clear that their eczema is due to pollen. This is probably caused by inhalation of pollen, and not by contact (see Contact Dermatitis), for scratch tests of the urticarial type are positive, and patch tests with whole pollen or with pollen oil, at least in my experience, which is only with children, are negative. Still another group of children has atopic derma­titis all the year round. Sometimes these children are sensitive to dust and wool, which accounts for their winter trouble, and also to pollen, which accounts for their summer trouble, and some may be sensitized to still other environmental allergens such as feathers and animal dander.

I have seen a boy of 7 years, whose eczema was caused solely and entirely by feathers. He lived on a chicken farm where there were 2,000 chickens. Food is sometimes a partial cause of atopic dermatitis in older children but I think environmental allergens are of far more importance. This has been emphasized especially in the last few years by Louis Tuft of Philadel­phia, and he has quite definitely caused exacerbations of atopic derma­titis by spraying house dust into the nose of one patient and ragweed into the nose of another. I have seen much atopic dermatitis due to wool, although I am not quite so enthusias­tic about it as is Dr. Earl Osborne²¹ of Buffalo, who has studied this sub­ject for years. I think that wool works more often by contact than it does by inhalation. Dr. Osborne has pointed out, however, that what we call “house dust” is to a large extent made up of wool fiber, and he is con­vinced that it works as frequently by inhalation as it does by contact. How­ever, scratch tests to wool are uncom­mon, and when they do occur, the degree of sensitization is low. Wool is a weak allergen, although rarely the degree of sensitivity is so great that simple contact of wool with the skin will cause urticaria, and I have seen one child who wheezed if a wool blanket came near his nose.

²¹Osborne, Earl D., and Murray, Philip F.: Atopic Dermatitis. A Study of Its Natural Course, and of Wool as a Dominant Allerg-enic Factor, Arch. Dermat. & Syph. 68: 619, 1953.

Such situations are, however, unusual. In 200 cases I found only one positive scratch test. Dust, however, in older children with atopic dermatitis gives a high percentage of positive scratch tests (I have no accurate figures) and many of these are strong reactions. Furthermore, it has been clearly shown that while dust is made up of all sorts of small particles, and that a good many of these are wool par­ticles, the allergenic activity of dust depends not so much upon these as upon its own specific allergen.

Children with wool sensitivity are likely to have eczema around the neck, on the wrists and the back of the hands (mittens), and around the ankles, if they have been wearing a snowsuit, and the legs get wet, as they usually do. There is also likely to be eczema in front of the elbows and back of the knees which is prob­ably caused by absorption of the allergen from other localities or pos­sibly by inhalation. Wool is also irritating to many skins entirely apart from any question of allergic sensiti­zation.

In a recent series of forty cases of “winter” atopic dermatitis in children between the ages of 2 and 12 years I found no positive scratch tests to wool, ten positive intracutaneous tests, and fourteen positive patch tests. There was no correlation between the posi­tive patch and intracutaneous tests- either might occur without the other.

Fig.  24.-Atopic dermatitis from wool.    Easily treated because it can be bandaged.    Tar paste is indicated,   or  Swartz’s  ointment made without lanolin.

A positive patch test* is pretty good evidence that the eczema is being caused by wool, a positive intracutaneous test probably means very little one way or the other. A nega­tive patch test, on the other hand, by no means excludes wool as a cause of the eczema, because in the patch test the element of rubbing is not present, which is probably of consider­able importance in causing the eczema. It is not easy to avoid wool. What I have usually done is to have the children wear Byrd cloth or nylon snowsuits, leather mittens lined with cotton, cotton or nylon jerseys, re­move wool rugs from their bedrooms, and either get rid of their wool blankets or have them enfolded in cotton sheets.

“The wool patch should be left on for five days. The sensitivity is of low degree, and it is rare for a positive test to show if the patch is removed in twenty-four hours.

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