3rd July, 20228 min read

Polymorphic light eruption: simple steps to cope

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Have you noticed that you get red, itchy or burning skin after you’ve been out in the sun? It could be polymorphic light eruption (PMLE) – a skin rash that’s triggered by sunlight or other ultraviolet (UV) light.

PMLE can feel very uncomfortable – and put a dampener on those summer activities we look forward to, such as beach trips and festivals. It may also leave you feeling self-conscious about how your skin looks.

So read on for all you need to know about PMLE, including the symptoms, who gets it and why it’s different to a ‘prickly heat’ type of rash. You’ll also find information on simple ways you can prevent and treat PMLE, and when you might need to see a doctor – to help make sure you can get out there for fun summer days.

What are the symptoms of PMLE?

The main symptom of PMLE is a skin rash that appears after you’ve been out in the sun.

What this rash looks like can vary from person to person – which is why it’s called ‘polymorphic’. Some people get a mild rash, while for others it can be more severe. Some people get it once or twice and others get it more often.

But usually, a PMLE rash:

  • looks like reddened skin, with tiny spots or small blisters (this may be less visible on darker skin)
  • feels sore, itchy and uncomfortable
  • appears within a few hours of being exposed to the sun – although it can appear after just 20 minutes, or up to 2 or 3 days later
  • appears on areas of skin that tend to be covered by clothes during the winter, such as your chest and upper arms and legs
  • gets better within a few days once you’re out of the sun (but may last up to 2 weeks) and doesn’t leave any scars

A PMLE rash may also slowly become milder as the summer goes on, as your skin adapts to being exposed to the sun.

Who is most likely to get PMLE?

PMLE is quite common – here’s what you need to know about who gets it:

  • research suggests you’re twice as likely to get it if you’re a woman
  • according to the BMJ, it affects about 1 in 10 people in the US. Other figures suggest it affects 10-20% of people living in western countries
  • it commonly starts between the ages of 20 and 40 – although it can happen at any age
  • it’s more likely if you have white skin – but it can affect people of all skin tones
  • about 15% of people who get it also have a family member who has it. But more research is needed to work out what genes are involved

What causes PMLE and when does it happen?

We don’t understand exactly why PMLE happens. But it’s thought that an immune reaction that happens in your skin when it’s exposed to ultraviolet A (UVA) rays in sunlight. (These are different from UVB rays, which cause

sunburn
).

This is why it’s common to first notice a rash in the spring – when you may be exposing your skin to sunshine for the first time in months – or if you visit a country that’s sunnier than where you live.

At first, if your skin gets more sun, the rash may get worse and spread. But if you continue to go out into sunshine – over the summer, for example – your skin may become more resistant to sunlight. This may mean you can stay longer in the sun without getting a rash.

Many people with PMLE find that their skin rash appears every spring and happens throughout the summer, before going away in the autumn.

What’s the difference between PMLE and prickly heat?

PMLE is sometimes mistaken for a

heat rash
, also known as ‘prickly heat’. But while it can look similar, prickly heat is caused by warm and humid conditions, rather than sunlight.

Plus, unlike heat rash, with PMLE your skin can sometimes adapt and become less sensitive to sunlight over time.

Read more about the symptoms of

heat rash
, or try our
Smart Symptom Checker
to get more information about any skin symptoms.

How to prevent and treat PMLE

Although PMLE can’t be cured, the good news is that there are things you can do to prevent it happening – and to treat the discomfort if you do get a rash.

Often, self-care measures and pharmacy treatments can help you manage your condition (although in some cases you may need help from your doctor).

Self-care measures

To help prevent PMLE, it’s important to manage your exposure to the sun, and to protect your skin when you’re out and about. So follow these tips:

  • try to stay in the shade as much as possible between 11am and 3pm, when the sun is at its strongest. And always get out of the sun before your skin starts to go red or burn
  • use a
    sunscreen
    that offers high protection against both UVA and UVB rays. Look for a 4- or 5-star UVA rating and a sun protection factor (SPF) of at least 50
  • apply a thick, even layer of sunscreen about 15 to 30 minutes before going out in the sun, and reapply it every 2 hours (and after swimming) – read more about
    how to apply sunscreen
  • remember that no sunscreen gives you 100% protection – so wear tightly-woven clothes with long sleeves, trousers or a long skirt, and put on a wide-brimmed hat to protect your face, neck and ears
  • gradually increase your exposure to sunlight in the spring as this can help to reduce the severity of any rash in the summer

Read more about

sun safety
and check out the
best types of sunscreen
to use.

Pharmacy treatments

If you get a mild PMLE rash, your pharmacist may recommend the following to help manage your symptoms:

  • staying out of the sun as much as possible
  • a mild
    steroid cream
    , such as hydrocortisone, to calm redness and soothe soreness and discomfort
  • antihistamine
    tablets to help reduce itching

In most cases, your rash will go away within a week or 2.

There is also some evidence that some antioxidant supplements, such as the fern extract Polypodium leucotomos can help. Some small studies suggest that using these before or after your first sun exposure may help prevent PMLE in the first place but discuss this with a pharmacist.

When to see a doctor

If the self-help and pharmacy treatments above don’t help, or you’re struggling to manage PMLE symptoms, or if you’re not sure what’s causing your rash, then see your doctor.

Diagnosing PMLE

If you have a rash at your appointment, your doctor will usually be able to diagnose PMLE from this, and a description of your symptoms and when they happen. It’s a good idea to take a photo of your rash, so you can show this to your doctor if it has gone by the time you see them.

In some cases, your doctor may want to do some simple investigations such as

blood tests
or a
skin biopsy
(where a small sample of your skin is examined under a microscope).

Occasionally, they may refer you to a skin specialist for further tests like a biopsy or rarely, phototesting. This tests your skin with different amounts and wavelengths of light, to see if they cause a rash.

Treatment from your doctor

If your rash is severe, your doctor may prescribe a short course of

steroid tablets
(such as prednisolone) to reduce skin inflammation.

Other possible treatments from a doctor or skin specialist include:

  • light therapy (phototherapy) – this involves exposing your skin to UV light in a special cubicle, and gradually increasing the strength of this light over time. It helps your skin become more resistant when it’s exposed to sunshine – it’s sometimes called ‘photo-hardening’, though it doesn’t make your skin any harder. Phototherapy is usually given in the spring, and you’ll probably need it every year, because the protective effects wear off
  • hydroxychloroquine – this is a tablet that suppresses your immune system and can help reduce the symptoms of PMLE
  • other medications – if the treatments above don’t help, a skin specialist may suggest other immune-suppressing medication, such as azathioprine

Long-term outlook

While PMLE can be uncomfortable and upsetting, it doesn’t cause any serious problems, and won’t lead to scarring or

skin cancer
.

The rash will usually go away without treatment once your skin is no longer exposed to sunlight. And many people find their skin improves over time. PMLE symptoms can also improve after the

menopause
(when you stop having periods).

However, if you have very sensitive skin, you may even get a PMLE rash in the winter. If PMLE is a longer term problem for you, the good news is that you can manage it well with the self-care steps and treatments mentioned above.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.