The onset of AD most often occurs in the first year of life between the ages of 3 and 12 months. Clinical criteria for AD established by Rajka and Hanifin and the UK Working party include three or more of itch, typical flexural distribution, patchy, excoriated erythema and personal history of atopy or atopy in a family member.1 Commonly there is also skin dryness. In children the rash is most often found on the face, cubital fossae and popliteal fossae (Figures 1a and b). The distribution and severity are highly variable, ranging from mild dryness and a minor rash on the arms and legs to total body involvement (Figure 2).
The itching of AD may be very disruptive, particularly during sleep. Severely affected children may wake up many times during the night, and parents often comment that the child’s sheets are streaked with blood from excoriations in the morning. Interestingly, small children often forget about the itchiness during waking hours until their clothes are removed, when they can literally go into a frenzy of scratching all over. Constant scratching often leads to areas of thickening of the skin. This is termed lichenification when it occurs in plaques and prurigo when it occurs in discrete nodules. Lichenification complicates AD, making it more challenging to treat.
Cutaneous infections are very common, not only because of constant scratching and disruption of the epidermal barrier, but because of inherent immunological and cutaneous abnormalities in these patients that increase susceptibility. The most common bacterial pathogen is Staphylococcus aureus, which causes areas of weeping, crusting and folliculitis (Figure 3). Chronic S. aureus carriage exacerbates eczema and is a much more common cause of treatment resistance than allergy.
In some cases, children with AD are also prone to relatively severe infections with herpes simplex virus. In contrast to most children, who may only ever suffer from stomatitis or herpes labialis, widespread or generalised infection with systemic upset may occur. Atopic children are probably not more prone than others to molluscum contagiosum, but the presence of this viral infection certainly exacerbates AD.
Environmental irritants and allergens
Children with AD are sensitive to environmental irritants and allergens, and this can include their topical therapy. It is well known that sand, wool, nylon, grass, soap and bubble bath cause irritation. Temperature changes and overheating are also problematic. Sometimes, even labels and rough seams in clothing can be a problem. Allergy to latex can be a little thought of trap for the unwary if caregivers are wearing gloves. It is common for these children to complain that their topical treatments sting and for their parents to comment that they cause erythema. This does not always indicate true allergy and may only be a problem when skin is excoriated and inflamed. The antiseptic triclosan in some bath oils can cause a cutaneous reaction that simulates a chemical burn. Although many patients with AD have raised IgE levels or positive skin prick test results to house dust mite, its role in causality and management is controversial and probably overvalued. Contact with grass and other airborne allergens such as animal danders, moulds and pollens can exacerbate AD.