Dermatitis is a general term to describe a group of common conditions presenting as itchy inflammation of the skin. The term eczema is often used interchangeably with dermatitis although theoretically eczema refers to atopic eczema. There are a variety of clinical types and causes.
Acute dermatitis is a rapidly evolving red swollen itchy rash that tends to weep and form blisters. Chronic dermatitis is a long-standing irritated thickened area of skin that can be red or darker in colour. The intermediate state is called subacute dermatitis.
Dermatitis skin can also split or fissure causing pain. Areas of crusting or tender blistering alert us to bacterial or herpetic infection complicating dermatitis.
The site affected depends on the specific type of dermatitis. See below.
Some specific types of dermatitis
- Atopic dermatitis
Atopic dermatitis is caused by many factors including a significant inherited component. The skin has poor skin barrier function, making the person more susceptible to developing dermatitis when exposed to environmental irritants/ allergens and during stressful periods. Infants commonly present with weeping crusted dermatitis on the face and neck. Older children and adults tend to have the creases of elbows/knees, wrists and ankles affected. The face or hands are often troublesome areas. There is an association in some people with asthma or hayfever.
- Irritant and allergic contact dermatitis
The site affected by dermatitis depends on where an offending substance contacts the skin. Irritant contact dermatitis is limited to the area of contact such as dermatitis under bandaids, whereas allergic contact dermatitis starts at the area of contact and spreads beyond the contact area.
- Seborrhoeic dermatitis
Seborrhoeic dermatitis is characterised by scaly red dry patches on the scalp, face and chest that are often not itchy. The condition can be worse during winter and during stressful periods. It is caused by an abnormal immune response to Malassezia yeast.
- Discoid eczema (nummular eczema)
This condition is characterised by coin-shaped itchy dermatitis patches on limbs and torso. Strong corticosteroids are often necessary to help settle the condition.
- Pompholyx (dyshidrotic eczema)
This condition is an extremely itchy blistering dermatitis on the hands and/or feet. It is usually triggered by heat and stress.
- Venous eczema (stasis dermatitis)
This condition is characterised by an itchy red weeping rash on the lower leg(s) of older people with varicose veins. The affected areas often have brown haemosiderin (iron) stains and sometimes leg ulcer(s).
- Perioral dermatitis
This is a common irritable red rash around the mouth caused by the use of strong corticosteroid or heavy cosmetics and skin care products.
- Xerotic eczema (asteatotic eczema/eczema craquele)
This condition is characterised by red patches of dermatitis in a background of dry irritable skin, usually on the lower legs. The skin can look like cracked pavers.
A number of genetic and environmental factors such as irritants and allergens are responsible. Stress, and sometimes food and medications, can trigger dermatitis. Atopic eczema is caused by many factors including a significant inherited component where an individual has a weak skin barrier due to a filaggrin gene mutation, making them susceptible to developing dermatitis when exposed to environmental irritants.
More than one type of dermatitis can occur in a person. For example, a person with atopic dermatitis may have her usual dermatitis on the bends of her elbows triggered by heat. The same person may also develop allergic contact dermatitis on her eyelids to fragrances in hair spray. She may also develop perioral dermatitis from using a heavy night cream or strong steroid cream around her mouth.
- Allergy patch testing is the gold standard for detecting delayed type allergy, for example, detecting hair dye allergy to the chemical paraphenylenediamine.
- Prick testing and the RAST test detect immediate type allergy such as urticaria (hives), rhinitis and asthma.
- A skin swab for bacterial/viral culture may be necessary if an infection is suspected.
- A skin biopsy may be necessary in some cases to exclude other causes of itchy skin.
The following guidelines are for atopic dermatitis and nummular dermatitis. Please refer to the specific dermatitis for others.
- Protect and improve skin barrier. Apply thick cream based or ointment based moisturiser at least twice a day. Avoid products with fragrances and plant extracts. Avoid irritants such as soap, shampoos, prickly materials, heat, friction and long hot showers.
- Control inflammation with intermittent courses of appropriate topical steroids. Weak topical steroids are used on the face, under arms and groins and stronger steroids are used elsewhere. Topical calcineurin inhibitor is also helpful.
- Cool compresses will calm the itch quickly. Use wet dressing over moisturiser and topical steroid for more severe dermatitis, especially if itch prevents the person from sleeping.
- Treat secondary bacterial infection with bleach baths, mupirocin ointment or oral antibiotics.
- In severe dermatitis, phototherapy and systemic treatment such as oral corticosteroids, cyclosporin, azathioprine, methotrexate and mycophenolate mofetil may be necessary.
Dermatitis usually responds well to irritants avoidance, moisturisers and topical steroids.
Referral to a dermatologist is advisable if a person’s dermatitis is not responsive to standard treatment within 4 to 6 weeks, if it causes significant distress and is interfering with sleep, school or work, if an allergy is suspected and if there are recurrent bacterial or viral infections.
This information has been written by Dr Elizabeth Chow