How do you get contact allergy?

Contact allergy, also called contact dermatitis or contact eczema, develops when the body’s immune system reacts against a chemical substance that is in contact with the skin. For example, an allergic reaction may occur to metals, preservatives, perfumes, colourings and many other substances found in consumer products, such as cosmetics and detergents. Many of the chemical substances are also found in the workplace, for example rubber (latex) is a frequent cause of disposable- glove allergy among nurses, nursing assistants and cleaning personnel.

The mechanisms

Whether you are affected by contact dermatitis depends on many factors. This means that the potency of the contact allergen (the substance that causes the allergy), the concentration of the allergen in a product, the frequency and length of contact with the allergen, for example soap, all play a role. Some people are more prone than others to contact dermatitis, but so far no specific gene has been found that increases the risk of allergy.

Contact dermatitis develops when chemicals penetrate the skin and are absorbed by cells from the immune system, the Langerhans cells. These cells communicate with the rest of the immune system by transporting the chemicals to the nearest lymph node (gland) where the chemicals then link with other cells in the immune system, the T-lymfocytes.

These T-cells become activated and change so that they are able to recognise, or ‘remember’, the allergy-causing chemical. The cells then divide, forming new, identical cells and they, too, can remember the culprit chemical. These cells go on to circulate throughout the body.
 

The process where a person becomes allergic to a substance is called induction–at this point there are no symptoms. But the next time that person comes into contact with a sufficient amount of the allergen an allergic reaction will occur. This is called provocation. This happens because the activated T-cells react to the invasive allergy-causing substance. The immune cells then release a compound called cytokines, which recruit other cells from the immune system and which are damaging to the tissue. The aim is to deactivate the unwelcome substance. During the release of the cytokines, the blood flow through the cell tissue increases, forcing out other fluids. When this happens the skin becomes red and may feel swollen. This is how acute allergic eczema begins.

The allergic reaction usually appears 18 to 48 hours after exposure to the allergen–it takes time for the cells to communicate with each other. Contact allergy is also called cell-mediated allergy or delayed allergic reaction. This is in contrast to anaphylaxis, which is a sudden, acute allergic reaction that can occur within minutes of coming into contact with the allergen and where antibodies are released into the blood. Anaphylaxis can be triggered by, for example, hay fever, asthma, or nettle fever. Anaphylactic shock, the most severe type of anaphylaxis, can lead to death in a matter of minutes if left untreated. Proteins such as pollen, house dust mites, animal hair and latex can cause anaphylaxis; it is not caused by chemical substances.

Symptoms and diagnosis

Symptoms of contact allergy

Eczema is the hallmark symptom of contact allergy, or contact dermatitis. With eczema the skin is red and swollen; there may also be small spots and blisters, causing irritation and soreness. If the eczema is left untreated, the skin will crack and become dry and flaky. This may lead to chronic eczema.


 

Copyright: Danderm

Eczema starts on the area of skin that has been in contact with the substance causing the allergy (the allergen). For example, eczema is first seen on the hands in cases of latex allergy caused by wearing latex gloves, or on the face when the person is allergic to the perfume in face creams.

If left untreated, the eczema, or contact dermatitis, will spread. Eczema can start on one hand, then spread to the other and then spread to other parts of the body, for example, the feet.

Untreated eczema can become chronic. This means that even if a person is no longer in contact with the allergen, the eczema may still continue.

The severity of the symptoms varies greatly from person to person. It depends on the type of eczema a person has and on whether he or she is particularly prone to the disorder.

Other causes of eczema

It is not only allergies that cause eczema. Constant irritation of the skin is another common cause of the disorder, for example, frequent hand-washing; prolonged use of cleaning detergents, industrial oils and solvents; and frequent or prolonged use of disposable gloves can all lead to eczema. This type of eczema is called irritant eczema or irritant contact dermatitis. It is not possible to tell if the eczema is cause by an allergen or an irritant just by looking at it. Your general practitioner will need to refer you to a dermatologist, who will then make an allergy test, a so-called patch test.

Often, allergic and irritant eczema occur together. This might happen with exposure to industrial oils, which contain allergy-causing substances and which can also irritate the skin. Deodorant is another example–this is a common cause of irritant eczema in the armpits and, as deodorant often contains perfumes, it can also cause allergic eczema.

Another common form of eczema is atopic eczema, sometimes called childhood eczema. Atopic eczema affects approximately 20% of children and in 90% of cases it starts before the age of four. Two out of three children grow out of the condition by the time they reach puberty. The cause of atopic eczema is unknown, but it is thought that genetic factors play a role as the condition often runs in families.

Atopic eczema is most commonly seen in the creases of the limbs, especially in front of the elbows and behind the knees and wrists, and on the ankles.

Atopic eczema in the elbow flexure
 

Although it is likely that atopic eczema is inherited, it is often environmental factors that trigger or worsen the disorder. Children affected by atopic eczema and adults who have had atopic eczema have very sensitive skin. This makes them react more easily than others to exposure to certain substances through, for example, frequent hand-washing, prolonged use of disposable gloves etc. Between 25% and 50% of people who have had atopic eczema in childhood, develop eczema on their hands later in life. Those with atopic eczema, both current and previous, have a greater likelihood of developing allergic asthma and allergic hay fever. In contrast, their likelihood of developing contact allergy is no greater than that of other people. Find out more about atopic eczema on:

www.atopiskeksemforening.dk (Danish link)

Contact allergy: its diagnoses

To diagnose contact allergy a patch test is used; this is also called a plaster test. The test is done either at a specialist dermatology clinic or at one of the dermatology departments at the university hospitals. When a patch test is done the person is tested with a small amount of the allergen that is suspected of causing the eczema. The allergens tested are in small foil pockets, or patches, on an adhesive strip. The strip is attached to an area of the body with little hair, usually the back, and remains in place for 48 hours. When the dermatologist removes the strip he or she can see if there is an allergic reaction on the skin under where the specific allergen was placed.

 

The patch test

The patch test usually tests 23 allergens. This is in accordance with the European standard series. The standard series includes metals, such as nickel, chromium and cobalt; latex; perfumes, or fragrances; preservatives; colouring agents; plant extracts; and treatment products.

In many case the European standard series is not sufficiently broad to give a precise diagnosis, and supplementary tests are often necessary. There are special tests targeted to specific occupations, for example, hairdressing. Standard testing can also be supplemented with products provided by the patient, such as cosmetics, samples from gloves, certain plants etc.

If the results of the patch test are positive, the dermatologist follows this up with a detailed investigation into the patient’s health to find out when and where the first contact with the allergen took place. Sometimes it is necessary to look into the list of ingredients on cosmetics and cleaning agents and products used in the workplace; and to make further tests or chemical analyses of the various products.

This is how any environmental causes of the eczema can be pinpointed. Knowing what these causes are plays an important role in preventing any new flare-ups or worsening of the eczema. Nevertheless, it is a difficult process and one that does not always lead to an explanation.

 
It may have been many years since the patient was exposed to the allergen and it is no longer a direct cause of the current eczema. An example of this is nickel allergy, which often occurs in puberty as a result of teenagers tending to wear inexpensive jewellery containing nickel.

Wherever possible, avoid the substance you are allergic to, as this will prevent the worsening of any symptoms.

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