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Atopic dermatitis affects about 15 percent of infants and small children, but it usually clears before adulthood. It may reappear at any time however.

Eczema is probably the result of an inborn defect of immune cells that tends to run in families; other family members often have asthma or hay fever. Atopic eczema is not contagious and does not affect one's general health. The skin is usually dry and easily irritated by soap, detergents and woollen clothing. Eczema may be aggravated by hot weather and a wide variety of environmental factors both at home and at work. These include dust, cats, emotional stress, and rarely foods. Teenagers and adults with eczema should choose their occupation carefully, in particular avoiding careers which involve wet work or handling detergents and solvents.

Atopic eczema rarely develops in babies before the age of four months (infantile seborrhoeic eczema occurs before this). The face is often affected first, then the hands and feet. Sometimes dry red patches appear all over the body.

In older children the skin folds are most often affected, especially the elbow creases and behind the knees. In adults the face and hands are more likely to be involved.

Sometimes there is secondary infection with staphylococcus aureus bacteria (impetigo). The result is oozing, crusting, with pustules, and the eczema may suddenly get worse. Infection with Herpes simplex (the cold sore virus) may cause a severe blistering rash.

Uticaria (see image above)

Urticaria refers to a group of disorders in which wealing occurs in the skin. The release of chemicals such as histamine causes small blood vessels to leak and results in tissue swelling. The weal's can be a few millimetres or several centimetres in diameter, coloured white or red, often surrounded by a red flare, and frequently itchy. Each weal may last a few minutes or several hours, and may change shape. Weals may be round, or form rings, a map-like pattern, or giant patches.

The surface weals may be accompanied by deeper swelling of eyelids, lips, hands and elsewhere. The swelling is called angioedema. Angioedema may occur with or without urticarial weals

Generalised urticaria

Generalized urticaria (hives) is often classified according to how long it's been present.

• Acute urticaria is of recent onset (hours, days or a few weeks).
• Chronic urticaria has been persistent for several months or years.

Urticaria may not be present all the time. Some find it more noticeable at certain times of day, or when they are warm or emotionally upset.

Acute urticaria is sometimes due to allergy. Allergy depends on previous exposure to the material, and the development of an immune reaction to it. A protein called IgE is involved.

The cause of an allergy may be:

• Medicine: most often an antibiotic, but many other drugs have been reported.
• Food: tiny amounts of fish, eggs, nuts or chocolate.
• Bee or wasp stings.

Most allergies are mild, but very allergic individuals may develop serious anaphylactic shock within a few minutes of exposure. The most frequent causes are antibiotic injections, bee stings or ingestion of peanuts. anaphylaxis results in urticaria, a tight chest, wheezing (bronchospasm), faintness and collapse. Medical attention must be sought urgently. A subcutaneous adrenaline injection will usually be given: those prone to anaphylaxis should carry an emergency supply (an EpiPen).

Most cases of urticaria are not due to allergy histamine and other vasoactive chemicals can be released into the skin for many reasons. Urticaria can occur the first time that a person is exposed to the material.

Some non-allergic causes of urticaria:

• Infection, including sinusitis, helicobacter (a cause of stomach ulcers), dental abscess and candida (thrush).
• Serum sickness, due to blood transfusion, viral infection or medicines (e.g. Ceclor); urticaria is accompanied by fever, swollen lymph glands, painful joints and nausea.
• Non-allergic reactions to medicines (especially morphine, codeine, quinine, aspirin and other non-steroidal anti-inflammatory drugs).
• Non-allergic recurrent angioedema, also provoked by medicines (particularly ACE inhibitors such as captopril, quinapril, enalapril and others).
• Non-allergic food reactions (most often from salicylates in fruit, azo dye food colouring, benzoate preservatives and other food additives).

Chronic urticaria is most often due to autoimmune disease (allergy to one's self), and may be associated with other autoimmune conditions such as thyroid disease. Circulating 'anti-idiotypic' antibodies cause excessive release of histamine.

Recurrent angioedema without urticaria may be due to C1 esterase deficiency (the protein C1 INH is missing or abnormal); there is often a family history of similar problems.

Reduce contact with irritants

• Keep cool: have tepid baths, wear loose cotton clothing, and keep bedding to a minimum
• Avoid direct skin contact with rough fibres, particularly wool
• Avoid dusty conditions
• Use gloves when handling chemicals, solvents and detergents
• Choose cosmetics carefully; make-ups, perfumes and creams can all irritate
• Bathe without soap: use water alone or add a soap-free cleanser

Reduce exposure to allergens

Allergic reactions can occur to materials touched, inhaled or ingested. Responsible compounds (detected by prick tests) include house dust mite, moulds, grass pollens and animal danders, such as cats and horses. The home, especially the bedroom, should be kept as free of dust as possible. It is controversial whether it's better not to have any pets or whether regular exposure to them reduces the reactions.

Most individuals will not helped by special diets (eg. dairy-free etc.). It is particularly important that growing children have a broad range of nutritional foods. But, if a particular substance consistently aggravates the skin problem, it is reasonable to avoid it for a while. Professional advice can be obtained from a registered dietician. Children are seldom allergic to dairy products and eggs although occasionally they may aggravate their eczema or result in hives, vomiting, diarrhoea, nasal stuffiness or wheezing. Others have flare-ups with wheat, nuts, food additives or other items. Fortunately, most affected children grow out of their food intolerance.

Other subjects may have contact allergic dermatitis, which can be detected by patch tests. The commonest contact allergy is to nickel (affecting about 10 percent of women). Other common contact allergies are rubber, perfumes, preservatives and certain plants.