Contact dermatitis

Contact dermatitis is inflammation of the skin caused by direct contact with a substance.

Contact dermatitis can be split into two types known as irritant and allergic:

• Irritant contact dermatitis: involves skin inflammation via direct physical or toxic damage to skin cells.
• Allergic contact dermatitis: involves skin inflammation via an underlying allergic process (type 4 delayed hypersensitivity reaction). Allergy usually develops after an initial sensitisation event.

We will see below that certain occupations put people at increased risk of contact dermatitis, due to exposure to irritants and/or allergens. Both types of contact dermatitis usually cause itching, erythema, vesicles or bullae, dryness or scaling of the skin. The mainstay of treatment for contact dermatitis is to avoid the irritant or allergen causing the inflammation, although other medical options are available.

Contact dermatitis is also known as contact eczema.

Below are some helpful definitions in the context of contact dermatitis given the overlapping terms that may be used.

• “Contact” = caused by something that comes into contact with the skin
• “Dermatitis” = inflammation of the skin
• “Irritant Contact Dermatitis” – contact dermatitis caused by an underlying irritant process. Since this involves direct irritation to skin, there is no need for a sensitisation event; dermatitis can develop on the first exposure.
• “Allergic Contact Dermatitis” – contact dermatitis caused by an underlying allergic process. Since this is an allergic process, it usually involves an initial sensitisation to an allergen, with dermatitis developing on subsequent allergen exposures.
• “Atopic Dermatitis” – also known as Atopic eczema. Atopic dermatitis is a separate condition from contact dermatitis. People with atopic dermatitis can place people at increased risk of contact dermatitis.

Worldwide, 1 in 5 people suffers with contact dermatitis.

Most cases of contact dermatitis are irritant (80%), with 20% of cases being allergic.

Unsurprisingly, people who work in occupations involving exposure to irritants and allergens are more likely to develop contact dermatitis. Occupations in which contact dermatitis is most common include:

• Beauticians
• Cooks and those working in food production.
• Florists, Horticulture, Agriculture.
• Hairdressers and barbers
• Healthcare (including dentistry)
• Engineering – especially those working with petrochemicals and metals.
• Cleaners

In the UK, contact dermatitis of any kind (including irritant and allergic types) affects roughly 1 in 5000 workers.

The hands are the most commonly affected body part:

• 75% of all contact dermatitis involves the hands.
• 90% of occupational contact dermatitis involves the hands.

Patient with a background of atopic dermatitis are at increased risk of irritant contact dermatitis (and possibly also allergic contact dermatitis). This is because atopic dermatitis involves disruption of the skin’s natural barrier, which means irritants (or allergens) can more easily reach deeper layers of the skin where they cause a reaction (see Aetiology and Pathophysiology below).

There are broadly two main types of contact dermatitis: irritant and allergic.

The umbrella term ‘contact dermatitis’ does include other rarer types of contact dermatitis, which are beyond the scope of a non-specialist. Rarer types of contact dermatitis include chemical burns, contact stomatitis and contact cheilitis, protein contact dermatitis, and systemic contact dermatitis.

Contact dermatitis can also be classified as acute or chronic:

• Acute: a single episode, with skin changes in keeping with acute inflammation.
• Chronic: persistent or repeated episodes of dermatitis, with skin changes in keeping with repeated or prolonged inflammation.

Irritant contact dermatitis affects the epidermis of skin.

Irritant Contact Dermatitis

A variety of irritants may lead to contact dermatitis. These can include:

• Rubber-related materials
• Prolonged water exposure (e.g. >2 hours per day)
• Hard or heavily chlorinated water
• Detergents
• Soaps
• Oxidizing agents (e.g. bleach)
• Acids and Alkalis

Irritant contact dermatitis affects the outer layer of the skin known as the epidermis. This is because irritants disrupt the natural skin barrier (i.e. the stratum corneum). This can occur by:

• Removing oils from the stratum corneum (e.g. solvents such as acetone remove lipids)
• Removing natural moisturising factors from the outer layers
• Damaging to skin proteins (e.g. sodium laurel sulfate can damage keratin and profilaggrin)

Disruption of the stratum corneum allows irritants to penetrate down into deeper layers of the epidermis. Once irritants reach deeper in the epidermis, they can directly damage keratinocytes, and also stimulate an inflammatory reaction.

Allergic Contact Dermatitis

Common examples of allergens that can result in dermatitis include:

• Metals (e.g. Nickel)
• Personal care products (e.g. preservatives used in cosmetic products; fragrances used in perfumes and body washes; nail varnish; and hair dyes).
• Topical medications (e.g. antibiotics and steroids)
• Plants (e.g. sunflower)

Allergic contact dermatitis affects the epidermis in 3 phases:

1. Hapten penetration and protein binding: small chemical molecules that penetrate the skin barrier. Not immunogenic on their own, but once past the skin barrier they form covalent bonds with proteins in the skin. These hapten-protein complexes are immunogenic
2. Sensitisation: Langerhans cells are immune cells which are predominantly found in the stratum spinosum. They recognise the hapten-protein complex, endocytose and process them, and then present them on their surface thus becoming an antigen-presenting cell. These cells then migrate to regional lymph nodes and specific T-lymphocytes are activated. These T cells distribute throughout the body after clonal expansion and can react on rexposure.
3. Elicitation: The elicitation phase occurs on re-exposure to the hapten leading to activation of the primed T-cells. Activation leads to proliferation of CD8 T cells, keratinocyte apoptosis, release of pro-inflammatory cytokines and ultimately a localised inflammatory response.

A thorough history is a vital part of diagnosing contact dermatitis.

History

The following parts of the history are particularly important:

• Presenting complaint (e.g. what is the main symptom?):
  • Itching, burning and stinging, all point towards contact dermatitis
  • In irritant contact dermatitis, burning, stinging and soreness might predominate
  • In allergic contact dermatitis, itch might predominate.
• Affected sites:
  • Irritant contact dermatitis is almost always confined to the body part in contact with the irritant substance.
  • Allergic contact dermatitis is usually confined to the body part in contact with the allergen but may spread to other areas.
• Onset / timing (consider the temporal association with owrk to determine if it is occupational):
  • Irritant = onset is immediate – 48 hours after exposure. Resolution usually quick (e.g. within 4 days of last exposure)
  • Allergic = onset is 24 – 72 hours after exposure. Resolution is longer in allergic dermatitis.

Remember, patients can develop allergic contact dermatitis to an allergen even if they have been in contact with that allergen for years without any issues. For this reason, a history of long-term exposure to an allergen does not rule out contact allergy. It is also essential to determine is there is any history of atropic dermatitis/eczema personally or in the family, and the type of occupation.

Examination

The appearance of both irritant and allergic contact dermatitis is highly variable. Furthermore, all types of dermatitis (irritant contact, allergic contact and atopic dermatitis) can appear similar.

In general, acute contact dermatitis of any cause presents with skin that is:

• Red (erythematous)
• Blistered (with vesicles or – less commonly - bullae)
• Dry
• scaly

Chronic contact dermatitis presents with skin that is:

• Very dry
• Cracked and fissured
• Lichenified (thickened)
• Scratch marks (excoriation)
• Hypo or hyper-pigmentation.

Certain features on examination might point towards irritant contact dermatitis. Dermatitis between the fingers (interdigital dermatitis) is known as ‘the sentinel sign’. This is a classic presentation of irritant contact dermatitis in the hands, and is commonly caused by prolonged contact with water. ‘Ring dermatitis’ i.e. changes to finger skin in contact with a metal ring – is suggestive of metal irritant contact dermatitis.

It is often possible to diagnose both types of contact dermatitis on history and examination alone.

There is no specific test for irritant contact dermatitis.

For allergic contact dermatitis, patch testing is the gold standard investigation.

Patch testing

On patch testing, the clinician chooses which allergens to test. A 'standard test' of allergens exists, which is usually applied to all patients. In addition, specific allergens may be selected based on the patient’s history. For example, if the patient works as a hairdresser, allergens which are common in hair products may be added to the test.

Once chosen allergens are applied to the skin – usually on the back – in an ordered grid. Each allergen is held in its own small aluminium disc which prevents the allergens mixing. A note is made of which allergen has been placed in which position on the grid. After 48 hours, the allergens are removed. The skin is then inspected 48 hours after allergen removal (i.e. 96 hours since allergen application). If any of the allergens are responsible for contact dermatitis, the skin in that part of the grid should show changes in keeping with acute inflammation (e.g. erythema, vesicles, oedema).

Management of contact dermatitis usually involves avoiding the trigger or minimising contact, and applying medical skin treatments.

We will consider management in four sections:

1. Trigger Avoidance
2. ‘Damage Control’
3. Medical Treatment
4. Dermatology Referral

Trigger Avoidance

The ideal treatment for contact dermatitis is:

1. Identify the offending agent
2. AVOID the offending agent

Many cases will resolve within three weeks after the last exposure to the offending agent; occasionally, it may take as long as 8-12 weeks for full resolution.

‘Damage Control’

If the offending agent cannot be avoided, then measures should be implemented to minimise skin damage:

• Minimise contact with the offending agent (e.g. use PPE, wash hands soon after exposure (with pH-balanced cleanser)
• Maximise the skin’s natural barrier: this is because contact dermatitis damages the natural skin barrier. Examples include pre-work barrier cream and post-work emollient cream
• Practise good general skin care: regular emollients, avoid hand washing with soap and instead use pH-balanced cleanser, dry skin carefully after washing.

Medical Treatment

Simple treatments which can be considered in primary care include:

• Topical corticosteroids
• Short course of systemic corticosteroids (e.g. oral prednisone)

Dermatology Referral

Consider referral to specialist secondary care if:

• Contact dermatitis is severe, recurrent or persistent
• Is difficult to treat
• Is associated with an occupational exposure

The employer has a duty to report contact dermatitis to the Health and Safety Executive. The doctor treating the patient has a responsibility to confirm the diagnosis and alert the employer. Dermatologists may consider starting specialist medical treatments (e.g. ciclosporin or azathioprine), but these are beyond the scope of a non-specialist.

Contact dermatitis can cause a reduced quality of life and low self-esteem.

We can divide complications in psychological and dermatological:

• Psychological: reduced quality of lfie (due to activity limitation and discomfort), loss of sleep (e.g. pain, itching), lowered self-esteem.
• Dermatological: Secondary skin infections such as impetigo or cellulitis, and Post-inflammatory hypo- or hyper-pigmentation.

NOTE: pigmentation changes occur particularly when contact dermatitis is chronic or left untreated for long periods of time.

Last updated: September 2024

References:

• UpToDate. Clinical features and diagnosis of allergic contact dermatitis.

• UpToDate. Irritant contact dermatitis in adults.

• DermNet. Contact Dermatitis.

• DermNet. Patch Tests.