Chronic actinic dermatitis

Written by Dr James Ferguson, consultant dermatologist

What is chronic actinic dermatitis?

Chronic actinic dermatitis (CAD), sometimes known as photosensitivity dermatitis/actinic reticuloid syndrome (PD/AR), is a condition in which the skin becomes inflamed, particularly in areas that have been exposed to sunlight or artificial light.

In addition, the majority of CAD patients have allergies to some substances that come into contact with their skin, particularly various flowers, woods, perfumes, sunscreens and rubber compounds.

Who is affected by it?

The condition particularly affects men over the age of 50, but also arises in women and is increasingly found in young male or female patients with atopic eczema.

Is it serious?

This is not a life-threatening condition, but it does require significant changes in lifestyle to avoid contact allergies and intense sources of light.

Why does the condition develop?

Although the cause is not known, it is suspected that the body's defence system over-reacts to substances within the skin that are made 'allergic' by ultraviolet and visible light.

Will it go away?

Many patients are spontaneously cured, but this may take several years and in the intervening period, patients have to learn to live with the condition, managing it by minimising their exposure to ultraviolet and visible light as well as chemicals.

How is the condition diagnosed?

Because the photosensitivity involves non-sunburn wavelengths of light (longwave ultraviolet and visible wavelengths), patients can develop the problem even on cloudy days, and windows and clothing offer no protection (unless the clothing totally blocks the light out).

As a result, it is not always obvious that light is the source of the problem, and doctors may have difficulty in diagnosing the condition. One helpful tip is to check the parts of the patient's skin that are not exposed to light, such as under a watchstrap, to see if the condition is present there.

Investigations to confirm the diagnosis

Phototesting using specialised equipment is possible in some university dermatology centres. Phototesting consists of having areas of skin exposed to known amounts of light of specific wavelengths and then looking at the reactions with comparison to the average population response. This procedure is painless and can be repeated to assess improvement.

Patch testing, another way of confirming CAD diagnosis, is conducted by most dermatologists. A range of chemicals is applied to the skin and left for two days. The skin is then assessed for reactions.

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