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Contact Dermatitis


What is a 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.

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.

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:

  • burns/scalds
  • 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 commonest allergens are:

  • nickel
  • fragrances
  • rubber
  • some plants
  • formaldehyde
  • skin medications (including topical corticosteroids)
  • hairdressing chemicals.

As with the irritant type, allergic contact dermatitis is more common in atopic individuals.

What causes contact dermatitis?

Irritant contact dermatitis

Irritants cause direct injury to the skin. This can occur over a short (acute) or long (chronic) period of time.

Acute irritant contact dermatitis

A single exposure to a substance causes an acute dermatitis, within minutes to hours after exposure.
The course of events is:

Blisters often heal spontaneously. Treatment will vary, depending on the cause. Some general guidelines for first-aid may include:

  • Irritant substance penetrates the skin.
  • substance damages the membranes of skin cells.
  • cell damage prompts release of chemicals that trigger the immune system into action. This is called an inflammatory response. The chemicals involved (inflammatory mediators) include lysozymes, prostaglandins, histamine and kinins.
  • some inflammatory mediators cause increased blood flow while others attract further inflammatory mediators.

Chronic irritant contact dermatitis

This is due to multiple exposures, often to several irritants at low levels over time. This dermatitis can take many months or years to appear. The course of events is:

Blisters often heal spontaneously. Treatment will vary, depending on the cause. Some general guidelines for first-aid may include:

  • each exposure adds to the gradual disruption of the outer layer of skin.
  • each time, inflammatory mediators are released.
  • the top layer of skin (epidermis) gradually thickens.
  • the lipid (fat) layer in skin is gradually damaged.
  • affected skin loses its ability to function as a barrier, so further exposure to an irritant produces further damage, and a 'vicious cycle' ensues.
  • the final result is dryness, scaling and thickening of the skin.

Allergic contact dermatitis

This is a type of immune reaction known as 'type IV' or 'delayed hypersensitivity' reaction. The characteristic feature of this immune response is a delay between first exposure to an allergen and the subsequent reaction. It, therefore, occurs in two stages, sensitisation and elicitation.

Sensitisation phase

This starts with the substance penetrating the skin, which then binds to Langerhans' cells (a type of skin immune cell), which then leave the skin and travel to lymph nodes (glands) nearby. Here, the allergen is shown to another type of immune cell, T-lymphocytes, which proliferate and produce 'memory' cells that can remember that particular allergen.

Elicitation phase

Once sensitisation has occurred, subsequent exposure to the allergen causes the T-lymphocytes to recognize the allergen, which activates them and causes them to multiply. Inflammatory mediators are released that induce the features of inflammation and bring more T-lymphocytes to the site of exposure. This ongoing immune reaction results in the eczema-like inflammation of the skin at the site of contact. This phase occurs within 48-72 hours after exposure. Small amounts of allergen can be enough to cause an inflammatory reaction.

What are the Symptoms?

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.

In contrast to irritant contact dermatitis, the reaction can extend beyond or occur in a different place from the site of contact. Occasionally, the appearance is that of urticaria (severely itchy raised red patches or wheals that can resemble insect bites, although these may be more irregular in shape). 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.

Timing

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.

Body site

Contact dermatitis usually starts in and often remains localized 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).

LOCATION OF CONTACT DERMATITIS AND SUSPICIOUS AGENTS

Location

Suspicious agent

Eyelids

Eye makeup, airborne substances, nail polish

Earlobes or neck

Metal jewelry

Forehead and hairline

Hair dyes

Face

Cosmetics (fragrance or preservatives), airborne substances

Armpits

Deodorants

Hands

Gloves, occupational hazards

Waistband

Elastic or nickel in belt or trouser stud

Feet

Shoes - leather, plastic, glues

All people who have an unusual dermatitis or one that resists treatment should have patch testing to test whether certain contact allergens are aggravating the dermatitis.

what else could it be?

Several types of eczema-like reaction can produce a similar appearance:

  • atopic eczema
  • seborrhoeic eczema (also know as seborrhoeic dermatitis)
  • discoid eczema
  • pompholyx (small water blisters on the hands and feet)
  • stasis or venous eczema
  • asteatotic eczema

Confusingly, any of the above conditions can be exacerbated by an allergic or irritant component.

Other skin conditions that should be considered are:

  • Drug eruption - usually suggested by a history of a rash that occurs after starting a new drug treatment.
  • Fungal infection - scrapings of the skin can be taken and examined under a microscope to make the diagnosis.

WHAT CAN YOU DO?

Prevention

  • 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.

Determine the cause

  • 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.
Treatment
  • 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.

WHAT CAN YOUR DOCTOR DO?

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 or if the dermatitis is long standing, you will need drug treatments. 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.

WHAT CAN YOUR DERMATOLOGIST DO?

For some patients, a referral to a skin specialist (dermatologist) is needed. The dermatologist will:

  • 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 aluminum 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.
  • Suggest ways of avoiding contact with the substance.
  • Suggest how to minimize exposure if avoidance is not possible, using:
    • Protective clothing
    • Barrier creams (the use of barrier creams is controversial). Their efficacy varies depending on the constituents of the cream and the specific irritant. In general, barrier creams are a poor substitute for gloves. However, their use reminds both the employer and employee about the potential link between their job and dermatitis.
  • 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.
  • Advise on suitable treatment in case of active dermatitis:
  • Suitable moisturizers
  • Topical corticosteroids, which suppress the inflammatory reaction so should reduceredness, swelling and pain.

WHAT IS THE OUTLOOK?

Whether the dermatitis will settle or recur depends on several factors.

  • Can the cause be avoided? If it can, the dermatitis will usually settle within a week. If the irritant or allergen is widespread, eg nickel found in jewelry, studs, coins and keys, then minimizing exposure will help prevent recurrence. In some severe cases, a change in career should be considered.
  • Does the patient also have atopic eczema? If so, then the risk is higher for developing a contact dermatitis.
  • Body site affected. Hand contact dermatitis is often the result of several irritants and allergens and is more difficult to manage.
  • Speed of recovery of the barrier function of the skin.
  • Superimposed infection can prolong dermatitis.
  • Treatments used can themselves act as irritants or allergens and delay recovery. This can occur with topical antibacterial creams, the constituents of medicated bandages or with herbal remedies.

Written by Dr Virginia Hubbard, specialist registrar in dermatology and Dr Malcolm Rustin, consultant dermatologist.

References
Belsito DV. The diagnostic evaluation, treatment, and prevention of allergic contact dermatitis in the new millenium. J Allergy Clin Immunol 2000 Mar; 105(3): 409-20.
Leow YH. Contact dermatitis due to topical traditional Chinese herbal medication. Clinics in Dermatology 1997 Jul-Aug; 15(4): 601-05.
Mowad CM. Update on contact dermatitis. Advances in Dermatology 1999; 14: 61-86.

Last updated 01.08.2005

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