Contact dermatitis is inflammation that results from contact of an external substance with the skin.
Reviewed by Victoria Lewis
Contact dermatitis is a type of inflammation of the skin that’s either caused by irritants or allergens. It can be painful and itchy, and is often misdiagnosed as eczema. Some forms of contact dermatitis can even be hard to treat.
We look at the causes, treatment and prevention of both irritant contact dermatitis and allergic contact dermatitis:
What is contact dermatitis?
Contact dermatitis is inflammation of the skin that results from contact of an external substance with the skin. This can occur through one of two mechanisms: irritant or allergic.
- Irritant contact dermatitis
Irritants cause approximately 80 per cent of cases of contact dermatitis. An irritant reaction is caused by the direct effect of an irritant substance on the skin. An irritant substance is one that would cause an inflammatory reaction in most individuals when applied in sufficient concentration for an adequate amount of time.
Irritants are often encountered at work (occupational) although other common irritants are soaps, detergents, food and cement. Almost all workers in wet-work industries, such as hairdressing, cleaning, metal engineering, building-site work and horticulture develop some degree of irritant contact dermatitis.
Irritants cause approximately 80 per cent of cases of contact dermatitis.
Both sexes are equally susceptible to irritant contact dermatitis. Those with dry skins or who have one or more of the ‘atopic’ conditions (eczema, asthma or hay fever) are more likely to develop an irritant contact dermatitis. An irritant dermatitis is most likely to occur on the hands. Irritants cause direct injury to the skin. This can occur over a short (acute) or long (chronic) period of time.
- Allergic contact dermatitis
Allergic contact dermatitis accounts for the remaining 20 per cent of cases. In this condition, the cause of skin inflammation is a hypersensitivity reaction, acting through the body’s immune system, to a particular substance or group of related substances.
Allergic contact dermatitis has the following features:
- Previous exposure to the substance is needed to induce allergy
- The reaction is specific to one chemical or a group of similar chemicals
- All areas of skin that are in contact with the allergy-provoking substance (allergen) develop the rash
- Avoidance of the allergen will result in resolution of the rash.
The most common allergens are nickel, fragrances, rubber, skin medications (including topical corticosteroids and hairdressing chemicals.
What are the symptoms of dermatitis?
The signs and symptoms of contact dermatitis depends on which type it is. The main things to look out for are:
Irritant contact dermatitis
➡️ Acute: The appearance of acute irritant dermatitis can range from a mild reaction consisting of transient redness to a severe painful burn with blistering.
➡️ Chronic: Chronic irritant dermatitis often begins with a few patches of dry, slightly inflamed skin that become thickened with time.
Allergic contact dermatitis
➡️ Early: The features of eczema develop at the site of contact. For example, the first sign may be an itch under an earring or along a waistband that contains rubber. The itch can develop into an area of redness with swelling and even small blisters that weep. Rarely, swelling of the mouth and upper airways can occur, which is known as angioedema. This is serious and needs urgent medical attention.
➡️ Prolonged: If exposure to an allergen persists, the skin becomes drier, thicker and more scaly with a change in the pigmentation (colour).
How is contact dermatitis diagnosed?
The most important factor in making a diagnosis is the suspicion by you or your doctor that a substance in your environment is causing the dermatitis. Doctors should always think about the possibility of contact dermatitis when managing a patient with an eczematous (eczema-like) reaction.
Two features are key to differentiating contact dermatitis from other causes of an eczematous rash and to determine the offending substances: the timing of onset or exacerbations and the part of the body that is affected.
Two features are key to differentiating contact dermatitis from other causes are the timing and the part of body affected.
Contact dermatitis usually starts in and often remains localised to the region most in contact with the offending substance. The pattern of affected skin is a vital clue in the origin of the substance (eg, a rash shaped exactly like your metal belt buckle could indicate an allergy to nickel).
Allergic contact dermatitis usually occurs 48 to 72 hours after exposure, and will wax and wane depending on exposure. Improvement of dermatitis during weekends or holidays is in favour of an occupational origin for the offending substance.
Occurrence or worsening at weekends suggests a hobby or environmental allergen. Seasonal variation of dermatitis is seen in particular with plant allergens, which can also be aggravated by light.
How to to prevent contact dermatitis
✅ Use gloves and protective clothing when dealing with potentially irritant substances (even for repeated or prolonged exposure to water).
✅ Thoroughly clean your skin if you come in contact with potential irritants.
✅ Make a list of substances that come in contact with your skin.
✅ Record the timing of use of each substance and see if it relates to the timing of your dermatitis.
✅ Record the body area exposed to each substance and see if it relates to the site of your dermatitis.
How to treat contact dermatitis
Avoid the suspected irritant or allergen. This is sometimes not possible but use of protective clothing, such as gloves, can help. In some cases of occupational exposure, time away from work may be necessary.
Once the diagnosis is made, and suspicious substances have been identified, your doctor will advise you how to avoid the suspected/offending substance.
Avoidance often resolves the dermatitis but if this is difficult you will need drug treatments.
Avoidance often resolves the dermatitis but if this is difficult or if the dermatitis is long standing, you will need drug treatments. Use of soap substitutes and regular emollients is the mainstay of treatment. Corticosteroids in the form of creams and ointments can be applied to the affected area to reduce the inflammation. Antihistamine treatments can sometimes help with redness and itching, particularly with urticaria.
Can a dermatologist help dermatitis?
For some patients, a referral to a skin specialist, also known as a dermatologist, is necessary. The dermatologist will do the following:
✔️ Discuss possible offending substances.
✔️ Offer patch testing to check for allergies. Suspected allergens, including a battery of standard allergens, are applied usually to the back under aluminium discs or patches. These are left in place for 48 hours and then removed and the skin inspected. After a further 48 hours, the sites are inspected again. Reactions can range from mild redness to severe painful blistering. The results of the patch tests are then interpreted in the light of the history and possible previous exposure to the allergen.
✔️ Discuss sources of the irritant or allergen and the relevance to you. Often an information sheet will be given.
For some patients, a referral to a skin specialist (dermatologist) is needed.
✔️ Suggest ways of avoiding contact with the substance.
✔️ Suggest how to minimise exposure if avoidance is not possible, using protective clothing and/or barrier creams.
✔️ Discuss how a slight change in your work pattern may help. For example, a hairdresser with contact allergy to a constituent of permanent hair dye could avoid colouring and concentrate on cutting instead. A letter from your dermatologist to your employer may help. Sometimes a change in career needs to be considered