Sun Allergy

Dr. Sarkany is the Head of Photodermatology (sometimes called ‘Photobiology’) at St. John’s Institute of Dermatology in London. He also works at the Lister Hospital (Chelsea, London), and Shirley Oaks and North Downs Hospitals in Surrey.

By Dr. Robert Sarkany, FRCP MD, Consultant Dermatologist and Photodermatologist, London

A guide for people suffering from unpleasant skin reactions to the sun and to sunlight.

Many people suffer from unpleasant and uncomfortable skin reactions to sunlight.

There are, in fact, several different diseases, with different causes and treatments, which can cause reactions to sunlight.

The details of each light sensitivity disease are outlined below, but if you have a skin problem with sunlight, the key is to find the cause i.e. to diagnose which type of sun sensitivity you have.

Clues from the timing of your sun allergy reaction

How can my sunlight allergy be diagnosed and treated?

The Main Types Of Sun Sensitivity

• Polymorphic Light Eruption
• Light sensitive eczema.
• Solar urticaria
• Erythropoietic Protoporphyria
• Medication-Induced Photosensitivity
• Actinic Prurigo
• Xeroderma Pigmentosum (XP)

The first thing is to know how long after the sun exposure it takes for your problem to begin:

Clues from the timing of your sun allergy reaction

• If you have attacks of pain or itch immediately on sun exposure (within seconds or minutes) the most common causes of this type of reaction are:Medication- Induced Light Sensitivity, Erythropoietic Protoporphyria and Solar Urticaria.
• If you have an itchy rash that comes up a few hours after sun exposure and lasts a few days, the most common cause is Polymorphic Light Eruption.There are many rarer causes, all causing slightly different types of problems, including light-sensitive eczema, lupus and actinic prurigo.

Diagnosis and Treatment

How can my sunlight allergy be diagnosed and treated?

For the doctor, the first task is to diagnose the cause of the light sensitivity since treatments for the different diseases are completely different. Also the type ("wavelength") of light causing the problem is different in the different diseases, so a sunscreen which is useful in one disease may not be useful in another disease.

The medical specialty dealing with skin reactions to sunlight is called Photodermatology. It is a branch of Dermatology. In recent years, there have been advances in the understanding and the treatment of sunlight-induced skin problems.

What can your Dermatologist do for your sun allergy problem?

Working out the cause of the sun allergy depends a lot on what a patient tells the Doctor. For one thing, your rash (if you have one) may have disappeared by the time you are seen, so there is nothing to see any more.

What can be discovered during the Consultation: As well as the description of the attack (how the skin feels during an attack, which places are affected and what the rash looks like if there was one to see), the timing of the rash is crucial because timing distinguishes many of these diseases from each other. Did the rash take minutes or hours to come on after going out in the sun, and how long did it take to then go away? Once you have been assessed by your Dermatologist in the clinic, tests can be arranged.

Tests for patients with sun sensitivity: The tests done depend entirely on what has come out of the consultation. There are specialised blood tests (e.g. porphyrins, HLA typing, lupus serology) . there are also “light tests”. "Phototesting" involves using machines, particularly the "monochromator”, to test the reaction of skin to different types of light especially the various wavelengths of ultraviolet light. It is useful in some, but not all, types of sunlight allergy (especially chronic actinic dermatitis and solar urticaria). Phototesting is a specialized test requiring special equipment and expert technicians, and is not available everywhere, but there are some centres in the UK that provide it.
Treatment: Treatment depends not only on the diagnosis of the cause of the light sensitivity (see below for details) but also from finding which type of light is causing the problem so one can use sunblocks, and sometimes window film filters, to block out the wavelengths of light causing the problem.

The Main Types of Sun Sensitivity:

• Polymorphic Light Eruption
• Light Sensitive Eczema.
• Solar Urticaria
• Erythropoietic Protoporphyria
• Medication-Induced Photosensitivity
• Actinic Prurigo
• Xeroderma Pigmentosum (XP)