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Do I Have a Sun Allergy (Photosensitivity) or Is It Prickly Heat?

Lynsey has suffered from PMLE for years. She enjoys sharing hints and tips for others in the hope that they can find some relief.

Learn the difference between a sun allergy and prickly heat.

Learn the difference between a sun allergy and prickly heat.

How I Was Diagnosed With Polymorphous Light Eruption (PMLE)

I began to notice extreme reactions to the sun when I was 19. I remember a summer's day when I had used factor 50 sunblock and sat in the shade behind a garden shed, only to look like a lobster after half an hour later.

After years of hiding in the shade and wondering why I was always suffering during everyone's favourite season, I began to investigate exactly what was happening to my body every time I spent more than ten minutes in the sunshine.

My discovery led me to confirm what I had suspected all along: I am allergic to the sun. Ok, so not an extreme version or a life-threatening allergy (as Solar Urticaria can be), but it's still a pretty inconvenient condition to have.

Initially, I had simply self-diagnosed my sun allergy. I hadn't looked into it online or anything, but I had approached my GP who told me that it was "just prickly heat" and to take some antihistamines and stay out of the sun. I assumed my reaction was just a strong one, so I followed this advice for years. But it started to get worse. I was getting hives even when sitting in the shade. My hands were bumpy from light through the car windows. I was itchy the whole summer, which in Scotland is really only like two weeks' worth of sunshine; it was still so annoying! And so itchy. I used to scratch myself silly.

I tried all types of creams and potions to reduce the itch. I took various oral antihistamines and tried different steroid creams. Nothing helped. I was also sick of not going on holiday like normal people—the thought of stepping into a hotter country terrified me. I was far too Scottish to be in a sunshiney place!

So I decided to look at things logically. Long story short, I discovered that hardening my skin using sunbeds worked well for me. However, the skin cancer risk terrified me, and when I developed a funny-looking mole, I went to see a dermatologist. When I explained why I was using a sunbed and how I was going about it, he asked a few detailed questions, took a blood test to eliminate Lupus (an autoimmune disease that can present sun allergy as a symptom) and gave me a diagnosis of PMLE, as well as a treatment plan. I was no longer alone!

what prickly heat looks like

what prickly heat looks like

What Is Prickly Heat?

  • Prickly heat is an all-around term used by those who are typically of the older generation to describe any rash caused by the sun/hot weather. In medical terms, it is the name used for a heat rash or a sweat rash.
  • A sweat rash or heat rash will usually develop in any sweaty areas: underarms, behind the knees, in the creases at the tops of thighs, on the chest, under the belly, etc.
  • They are caused by heat simply because you sweat, and the area is not being dried off quickly enough, often due to clothing or body position.
  • The rash looks similar from person to person: small bumps under the skin alongside some reddening/inflammation; typically, the rash is itchy or prickly, hence the name prickly heat.
  • You do not need sunlight to get prickly heat/sweat rash/heat rash.


What Is Polymorphous Light Eruption (PLME)?

  • Polymorphous Light Eruption (PLME) is a reaction caused by UV rays on your skin. As the name suggests, its appearance can look different from person to person and even different from breakout to breakout.
  • It is estimated that between 5%-20% of the world population has it. According to the Cleveland Clinic, it occurs more in women than men and usually starts in their teens and twenties.
  • The rash may look similar to prickly heat but can also be blister filled or have hard lumps and will generally appear quickly after sun exposure—sometimes within hours of being outside.
  • Unlike prickly heat, it is not the temperature that causes the reaction but the actual sunlight. So, you can be in a hot country but not experience PMLE so long as you are not touched by the sun.

How Can I Tell the Difference Between PMLE and Prickly Heat?

There is little to really differentiate between the two simply by looking, which is why GPs can often misdiagnose these conditions. The best thing that you can do to determine what reaction you are having is to try to record your symptoms.

Make a diary, and include things like this:

  • What you were doing
  • What you were wearing
  • The time of day
  • Whether you were in direct sunlight or if it was secondary, i.e., sunlight through a window or a pool. Or if you were completely out of the sunlight when the rash developed.

This simple practice will help you quickly pinpoint the activities that bring out your rash, which is the first step in managing your symptoms. Avoidance is a good method—at least in the beginning. This will also be a great tool for your doctor during diagnosis.

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Bear in mind that you may not actually have either of these conditions. Only a dermatologist can help you to obtain an actual diagnosis. Save yourself years of torment and just speak to a dermatologist as they will save you so much misery and actually make a plan on how to commence treatment. I wish I had done this sooner.

What Causes PMLE?

  • According to the Mayo Clinic, the exact cause of PMLE isn't well-understood. The rash appears in people who have developed a sensitivity to components of sunlight, and in particular, ultraviolet (UV) radiation from the sun. This is known as photosensitivity, which results in immune system activity that causes a rash.
  • While there has been speculation of the cause, there really is no particular reason that people suffer from this reaction. At least, nothing that has been scientifically proven so far.
  • Some people have family members that have it too, which suggests a genetic link. Some are the only ones in their family with it, which suggests otherwise.
  • Some people have autoimmune disorders in addition to PMLE, suggesting it is part of the associated symptoms of their autoimmune disorder. Yet, others don't have an autoimmune diagnosis.
  • Some can attribute the onset of symptoms to taking a new medication or from, pregnancy or a change in diet. Others can't pinpoint exactly what changed when it began.
  • Some people have had it for life; others have had it develop randomly later in life.

As disappointing as it may be to hear, there is really no rhyme or reason why anyone gets PMLE, at least that we know of as yet.

Can Anyone Get It?


Surprisingly, this is not something that is limited to a particular region or race. There are more cases of it in countries with less sunshine—it seems to be pretty common here in the UK. But it seems that no one is really immune. Of course, if you live in a country with more sunlight, you are likely to be able to harden your skin more naturally, but it doesn't completely eradicate the possibility of you having PMLE just because you live somewhere sunny.

Here are some ways you can treat your itchy rash if you have PMLE.

Here are some ways you can treat your itchy rash if you have PMLE.

How to Treat PMLE

If you are unlucky enough to have a flare-up, there are a few things that you can do to try and reduce the itch. Generally, the rash will disappear within a couple of weeks if you are able to avoid being in the sun again. In the meantime, you can try some of these tips to ease the itching.

  1. Don't scratch: As hard as it is, this will just irritate and burn even more.
  2. Take a cool bath: This will help remove the heat from your rash. Try not to stay in there too long. You may catch a chill. Similarly, cold compresses help as well.
  3. Rub on aloe vera gel: This helps to cool and reduce itching.
  4. Use antihistamines: You can buy lots of over-the-counter versions, but you may require something a bit stronger. Speak with your doctor about getting something for skin allergies specifically.
  5. Apply some anti-itch cream: Something with hydrocortisone should help with the itching somewhat. You can buy this over the counter, but be careful not to use it too long as steroid creams can thin the skin if overused.
  6. Get a referral to Dermatology: Do this as soon as possible in order to arrange an effective treatment plan. I really wish I had done this sooner.
Staying inside is the best way to avoid PLME outbreaks.

Staying inside is the best way to avoid PLME outbreaks.

How to Prevent It

Unfortunately, there isn't any way to prevent the development of the condition itself, but you can certainly reduce the chance of itchy outbreaks. Please note, the following tips may not help everyone, and it is a bit of trial and error to find out what exactly helps you. PMLE is a very unique condition and affects us all in different ways.

  1. Cover up. As warm as it may be, covering your skin will help to reduce the reaction. You can even purchase UV-blocking clothing for this reason.
  2. Use a parasol. Not just limited to Victorian times, I have been in some European countries and seen ladies using UV umbrellas to protect them from the sun. Tour guides use them in particular. It's pretty effective and stops the sun beating down on you when out and about.
  3. Apply sunscreen. This will help any areas that cannot be covered, such as hands and feet. Use a high-rated sunscreen with a high SPF, apply at least half an hour before going out, and top up regularly.
  4. Live like a vampire. I know it's a terrible thought, but before I discovered my light treatment, this worked fairly well for me. Try to avoid the sunshine completely if you can. If this is not possible, try to avoid being in the sun between 10 a.m. and 2 p.m as this is when it is most intense. This even includes sitting at a window with the sun shining in.
  5. Avoid visiting sunny places. This sounds ridiculously obvious. But you should probably not visit any hot countries if you suffer from PMLE unless you have already hardened your skin beforehand. European countries in late Autumn are quite nice. Winter is a bit chilly, but it's not overrun by tourists, at least! Selling it?? No?? If you absolutely must go somewhere toasty, try to follow the advice above to try and reduce the chance of a breakout.

Long-Term Prognosis

PMLE overall is more of an irritating condition more than anything else long-term. Of course, there are some lifestyle limitations associated with the condition, and things may need a bit more advanced planning, but other than that, you can have a pretty normal life with it.

If you do opt for UV treatment, your risk of Melanoma will increase, but this is something you can keep an eye on by vigilantly checking for any changes and going to see a dermatologist with any concerns promptly.

Help and Support for People With PMLE

The best support that I have found is peer-to-peer support, namely, a Facebook support group. If you search PMLE on Facebook, you will find one, I'm sure. These groups are filled with advice, lovely people, and even just an understanding ear when you need to vent about wearing a full-length jumpsuit and wide hat to a wedding in the middle of summer!

Your dermatologist is the best medical support that you can have. GPs are unable to really help with such a specific condition unless they have had prior dealings with it. However, if you can find a dermatological specialist, they will be able to help you find a treatment plan that works best for you.

Your friends and family are also there to support you! Sure, you may get a few Dracula comments, but roll with them—a sun allergy sounds pretty extreme, doesn't it? The people around you will be a bit perplexed, but I have found that when you explain that no, it is an actual condition, and no, I don't actually enjoy skulking in the shadows, they tend to be more empathetic.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2019 Lynsey Hart


bhattuc on July 29, 2020:

Very informative article.

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