Polymorphic light eruption, also known as sun poisoning (which may give you some idea of how uncomfortable it is), is the most common form of sun allergy. It is thought to be caused by the immune system reacting to a change in a substance in the skin caused by exposure to UV light. It triggers an itchy or burning rash that can appear within hours of exposure to sunlight, or can flare up as long as two to three days after being out in the sun. It can last anything up to two weeks.
Polymorphic light eruption is thought to affect about 10 to 15% of the UK population and is often mistaken for prickly heat (see below). Most people experience polymorphic light eruptions after several hours outside on a sunny day, but others may find as little as a few minutes outside can trigger an angry rash!
What does polymorphic light eruption look like?
A rash usually appears on parts of the skin exposed to sunlight, typically the head, neck, chest and arms. It can manifest itself in different ways:
- A crop of red raised spots around 2mm to 5mm pink
- Some people may experience blisters that turn into larger, dry, red patches that look a bit like eczema.
- Rarely, the rash appears as skin patches that look like targets or bull's eyes.