Contact Dermatitis

It is extremely common for people to suddenly experience redness on the skin, coupled with intense itching. If, for instance, this is detected on the ears it could be attributed to a negative reaction to earrings or, in the case of it being on the wrist, a watch may be to blame. Less obviously, a rash on the neck may be down to nail varnish or even a match. All these are typical examples of contact dermatitis.

Contact dermatitis is a very common condition that, excluding accidents, are responsible for about 50% of all occupational health risks. It is a local inflammation of the skin caused by the influence of a foreign substance that comes in contact with it. The affected area presents a diffused redness and flaking accompanied by itching, the frequent presence of edema (swelling) and small blisters. If the symptoms persist, the skin becomes dry, cracked and scaly. The rash isn’t contagious or life-threatening, but it can be very uncomfortable.

Depending on the mechanism responsible for causing it, contact dermatitis can be divided into two major categories: allergic contact dermatitis and irritant contact dermatitis.

Irritant Contact Dermatitis

Irritant contact dermatitis is the most common type. This non-allergic inflammatory reaction occurs when a toxic substance, such as a detergent, damages the skin’s outer protective layer. Some people react to strong irritants after a single exposure. Others may develop signs and symptoms after repeated exposures to even mild irritants. Over time some people develop a tolerance to the substance.

Irritant contact dermatitis may affect anyone given sufficient exposure to substances that can trigger it. For example an acid will certainly cause an immediate intense inflammation upon any contact with it. Milder irritants such as soaps and detergents require higher concentrations and longer exposure in order to cause the same reaction. Greater sensitivity is shown in women as well as atopic individuals, i.e. those with a syndrome of allergic hypersensitivity that tends to be hereditary. People with an atopic tendency may develop any or all of three closely linked conditions referred to as the atopic triad; atopic dermatitis, asthma and hay fever (allergic rhinitis). Often these conditions run within families, with a parent, child or sibling also affected so knowing about any  family history of asthma, eczema or hay fever is particularly useful in diagnosing atopic dermatitis in infants. Irritant contact dermatitis is sometimes misdiagnosed as atopic dermatitis.

Irritant contact dermatitis accounts for 80% of skin diseases caused in the workplace. The most common causes are detergents, solvents, alcohol, mineral oil, petroleum, cement, adhesives, various acids and alkalis, etc.

Whereas In the home, the most typical case is the so called housewife’s eczema. This is caused by extensive prolonged exposure of the hands to washing up liquids, detergents and household cleaning agents. The skin becomes dry, rough and reddened, particularly over the knuckles. It may thicken, crack, flake and itch. Some people may find that soap gets trapped under any rings worn and this can trigger the disease. This is the place where the rash typically and commonly appears on the tips of the first, second and third fingers of the hand most frequently used. The fingers in this disease may look dry and red at the tips, there may be chapping on the back of the hands and palms may look dry, cracked and inflamed. This not only affects people in the home, but also those whose profession involves excessive use of soap and water such as bar and kitchen workers as well as surgeons and other medical personnel. It is of extreme importance in this case is to refrain from exposure to water for a substantial period.


Another case occurring in the home is a type of dermatitis called nappy rash, which is  found in the nappy area on babies – on the bottom, genitals, lower abdomen, or thigh folds. This is caused by prolonged contact of the skin with urine and faeces. Maintaining dry skin by frequent nappy changing as well as using a barrier cream helps solves the problem.

Allergic Contact Dermatitis

Allergic contact dermatitis differs from irritant contact dermatitis in the sense that it requires prior susceptibility of the individual to certain a substance to which you’re sensitive, known as a allergen. A reaction can either be a result of a single exposure to a strong allergen, or in the case of a weaker allergen, multiple exposures over time. Once your immune system has been “trained” to recognize the allergen, any contact with it in the future will result in induction of a gradual sensitivity reaction leading to dermatitis within 48 to 72 hours.

It should be noted that there are a lot of substances that can cause both allergic and irritant contact dermatitis.


The following materials and substances are often the main triggers of dermatitis:

Nickel – One of the most common causes is the metal, nickel. It is widely used in many metal products such as jewellery, buttons, zips, hook & eye fastenings, hair grips etc. The area that comes into direct contact with the metal will be affected – for example, under a hook & eye bra fastening, under a button on jeans, on the wrist below a watch strap, on ears because of earrings etc. In the case of newly pierced ears, earrings containing nickel should be avoided for at least the first 3 weeks. The allergic reaction to nickel is increased by perspiration, and thus is worse in summer.

Natural Rubber – It occurs mainly in those who wear rubber gloves, such as medical and paramedical personnel. Also, the rubber contained in most undergarments can cause a reaction as can footwear. Finally, dermatitis may even be caused by latex condoms. A reaction is often due to maceration of the skin, often associated with sweating under occlusion. Once the diagnosis of allergy to natural rubber latex is established, then avoidance by using non-latex materials is the best way to prevent reactions occurring. However, in practice, this is almost impossible since rubber is so widely used, although there are less likely to be problems from old rubber than new. The potential for rubber latex to elicit an allergic reaction (its allergenicity) decays with time and the most potent articles are those most recently produced, particularly if they are powdered.

Hair dyes – Some people experience sensitivity to Paraphenylenediamine (PPD), which is found in permanent hair dyes, especially those at the darker / black end of the range. About 25% of those affected also exhibit similar sensitivity to semi-permanent dyes. The use of natural henna or vegetable dyes would be a better option, but even these may sometimes contain azo-dyes that could cause a negative reaction. Clearly, the best solution is to avoid hair dye altogether.

Those sensitive to PPD exhibit cross-sensitivity to dyes used in clothing, especially dark colours. Therefore, it is advisable to wear light colours made from natural materials and wash new clothing at least 3 times prior to wearing to get rid of excess dyes. Finally, 25% of sufferers are allergic to certain local anaesthetics.

Chromium – This is included in cement, leather, some matches, paints, etc. An allergy to this metal can be easily identified in the use of jewellery containing it but can be much harder to diagnose when caused by products that are not made of metal. For example, chromium salts are often used in the making of leather during the tanning process, mostly for poor quality leathers. It can also be caused by smoke or ash from some matches. As it is also used in pigments, especially green or yellow, it can be found in clothing. Occupational exposure is common in construction workers, welders and in many industrial workers.

Cosmetics – Perfumes, lotions, creams, and make up products can include fragrances or preservatives that can cause an allergic reaction. Therefore, for sensitive skin, fragrance free products are a better choice as are ones with alternative preservatives and, where possible, those without altogether.  Another form of contact dermatitis is photoallergic dermatitis, caused when some perfumes and sunscreens react negatively with ultraviolet radiation. Dermatitis as a result of using nail varnish is particularly difficult to detect as it can cause a reaction in other parts of the body that have come in contact with it, such as the face or chest

Medications – Several forms of medication can be the culprit when they come in contact with the skin. Some of these are: the antibiotic neomycin, which is widely used in creams, sprays, and eye drops, antihistamines used to treat insect bites and, less frequently, local anaesthetics (eg in haemorrhoid treatments). In addition, an allergic reaction can be caused by excipients found in eye drops and locally applied slow release patches (e.g. nitroglycerin, nicotine, etc.).

Plants – Depending on geographical location, many plants can be found that cause dermatitis. A large number of plants are known to cause irritant contact dermatitis in many people when they come into contact with skin, some examples are stinging nettles, tulip bulbs, ivy, tomato plants, eucalyptus etc. Whereas other plants cause allergic contact dermatitis in certain people who have developed an allergy to them, poison oak, poison ivy, olive trees, onion and garlic are just a few of these. Certain plants can even cause a reaction in those allergic to them after simple exposure to their pollen carried in the wind. Sometimes a rash may develop without direct contact with the plant; this may be a result of their juices being on clothing or the fingers, e.g. with olive oil. Irritant sap or latex in a plant is often to blame, such as occurs with agave, daphne and buttercups. If you know you are allergic to any of these plants, you should, where possible, avoid exposure to them or wear protective clothing.

Detecting the Culprit

To determine the exact cause of allergic contact dermatitis, first the suspected diagnosis, along with a detailed history and distribution of the rash, must be established. Then the exact identification of  the allergen is achieved  by means of an epidermal assay, known as a patch test.

In this process, the dermatologist or allergist puts a minimum amount of 30 allergens in individual square plastic or round aluminium chambers.They are kept in place with special hypoallergenic adhesive tape, which is applied to the patient’s upper back and left undisturbed for 48 hours. In some cases a pre-made patch test, such as TRUE Test may be used, which is also applied for 48 hours, and in some cases 96 hours. Following this, the results are evaluated after 48 and 72 hours and recorded according to local inflammation in any allergen that caused a reaction. The test can be repeated with different allergens if the results are negative.


An alternative option is a radioallergosorbent test (RAST), in which  the presence of antibodies against specific antigens is detected by means of a blood test. This method has some advantages in terms of objectivity, patient comfort and, in the case of acute dermatitis, the ability to avoid unnecessary contact with allergens. However, more effective results are achieved with an epidermal test (patch test) is carried out by an experienced doctor.


The acute phase of contact dermatitis is treated like any other form of dermatitis, with the use of corticosteroid creams, ointments, moisturizers and, possibly, antihistamines. It is of primary importance, however, to avoid exposure to the responsible substance, especially during the acute phase as well as in the future.

Clearly the only way for symptoms to be eradicated and, in turn bring relief to a patient, is the permanent removal of the cause. However, since determining the exact source of dermatitis can be a lengthy process, it requires immense patience on the part of the sufferer and the dermatologist, as well as full cooperation if the root of the problem is to be found.

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