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Are You Allergic To The Sun? Polymorphous Light Eruption, Explained

A rash or allergic reaction can show up on your skin thanks to a huge range of things, but did you know you can actually get rashes from sun exposure? Yup! This phenomenon is called polymorphous light eruption (PMLE or PLE), and it can happen pretty frequently to people who are sensitive to sunlight.

In fact, this acquired condition is more common than you’d think! It’s also referred to as sun poisoning, and it’s typically experienced by young women. After menopause, women tend to get it less often, although children and males experience it as well. Doctors estimate that between 10% and 20% of the population may be susceptible to PMLE.

Is it dangerous? Painful? How do you treat it? Read on!

Polymorphous light eruption on legs

What is polymorphous light eruption?

Simply put, PMLE (also referred to as polymorphic light eruption) is a sun rash. The main areas that become affected are the parts of your body that are most likely to become exposed to the sun: the back of your hands, your arms, neck, chest, and lower legs and/or feet. It’s less common, but some people do get eye and lip lesions. Just 20 minutes of light exposure can trigger the problem, and a PMLE rash typically appears anywhere from a half an hour after you’ve been in the sun to a few days later, as a delayed reaction. Tricky, we know!

The “polymorphic” part of the name refers to the fact that the rash looks different for different people, although it generally appears in one clinical form for each individual.
PMLE can appear as:
+ Red papules – Small lesions that can be found either alone or in groups.
+ Erythema – Areas of red skin that result from increased blood supply.
+ Erythematous plaques – Thick, raised, red lesions, often made from papules growing together and surrounded by a border.
+ Lichenoid plaques – An eruption of red, circumscribed lesions that are mostly flat.
+ Targeted lesions – A dark center with a blister or crust that’s surrounded by a raised ring with fluid swelling (oedema) and a red outermost ring.
+ Dermatitis – Dry, red inflammation of the skin.
+ Vesicles, aka Blisters.
+ Prurigo – Intensely itchy spots that look like bumps (scratching these may lead to scarring).
+ PMLE sine eruptione – An itch, with no visible bumps or redness.

An example of PMLE, courtesy of dermnetnz.org.
Another example of PMLE, courtesy of dermnetnz.org.

As you can tell, PMLE will occur in a myriad of forms, and these symptoms are also common to other allergic reactions, so it’s important not to self-diagnose, and to see a professional who can properly asses your skin. If you have a PMLE reaction, you may also experience burning, itching, fever, and/or malaise. In severe cases, PMLE has been linked to distress, anxiety, and depression.

A third example of PMLE, courtesy of dermnetnz.org.

What causes PMLE?

Although researchers don’t know the exact mechanisms, PMLE happens when light generates an immune response in your skin, impairing your t-cell function and your cytokine production. T-cells are the white blood cells in your body that are responsible for some immune responses; Cytokines are substances designed to regulate the activity of other cells, and they are the ones that send cells towards the sites of inflammation, infection, and trauma.

There is a genetic element to PMLE, so it’s possible you’re more prone to it if your relatives have it. Tobacco may also exacerbate the problem. Mainly, though, PMLE is a result of hypersensitivity to the sun’s UV rays.

You probably already know that UVA and UVB rays from the sun cause premature signs of aging, eye damage, and skin cancer. UVB rays cause skin to darken by damaging the superficial layers of our skin. UVA rays are less intense, but remain strong all day and can penetrate clouds and glass. These sun rays make up about 95% of the ultraviolet radiation that reaches the earth.

Both types of UV rays cause PMLE, although UVA rays account for up to 90% of cases. Visible light frequencies, like fluorescent lights, can also cause PMLE in those who are super-sensitive.

A PMLE rash on the chest, courtesy of mayoclinic.org.

How can I tell the difference between PMLE, sunburn, and heat rash?

This is an excellent question, and one that most likely contributes to people not knowing they have PMLE.

The main difference is that PMLE and sunburn occur on skin that’s exposed to the sun, whereas heat rash occurs where the skin is covered. Heat rash happens when tiny little blisters block our sweat glands and cause the skin to redden, feel irritated and become itchy.

Sunburn is a result of the sun’s UVB rays literally damaging the top layer of our skin, called the epidermis. PMLE is your skin reacting abnormally to sun exposure.

An example of sunburn, NOT PMLE or heat rash.

Great, I think I have PLME. What should I do now?

For most people with PMLE, they have an initial reaction after their first time in the sun — usually in the spring or early summer, after their skin has been protected and not in contact with the sun all winter. The good news is that with additional exposure, you should be able to tolerate more sunlight without having a PMLE reaction. This happens as a result of your skin hardening and becoming used to light exposure. Unfortunately, this initial rash at the start of the summer is likely to continue throughout your life. That said, some people are lucky enough to see their PMLE gradually become less sensitive through their lifetime.

Unfortunately, there’s no general cure for PMLE. Corticosteroid creams and oral corticosteroids (prednisone) or antihistamines can help, as can steroids and hydroxycloroquine tablets. Doctors may also treat it with immune-suppressing drugs such as azathioprine.

A PMLE reaction on the arms, courtesy of dermnetnz.org.

Can you stop PMLE before it starts?

Yes, if you follow sun safety tips! We know, it’s a drag, but so is being covered in an uncomfortable and unsightly rash. Stay in the shade, wear hats and protective clothing, use a broad-spectrum sunscreen to protect from both UVA and UVB rays (ideally one with a high SPF, 50+) and reapply liberally — although everyone should be doing this, regardless! It’s important to note that sunscreen can only do so much to prevent a PMLE reaction, sun sunscreens are never 100% effective against UV rays, although a recent study did show that broad-spectrum sunscreens that were reapplied consistently gave the best protection.

Nutritional supplements may help if you have PMLE. Nicotinamide, or vitamin B3, vitamin E, and beta-carotene Vitamin D supplements have been shown to ameliorate PMLE.

If you suffer from PMLE, you may want to consider a desensitization treatment to increase your skin’s resistance to the sun. Start with just a few minutes of sun exposure in the spring, and gradually increase the amount of time spent outdoors. By the time full summer arrives, your skin will (hopefully!) have adjusted.

  1. Is it weird that I want to submit my PMLE rash pic for this ? My derm diagnosed it last year and of all the skin issues I have it’s made for that wildest photo 😂😂🙈🙈🙈. This article is super helpful though can definitely use it to share when I’m explain “my weird sun allergy”

  2. Is is possible to get this from laser hair removal? I have something that looks very similar and still hasn’t been diagnosed.

  3. My brother had this. It was the result of having porferia. He didn’t get that diagnosis until months before he died. However he spent at least 15 miserable itchy years without correct info.

  4. Sooo these rashes/hives just started this October with me. I’m 24 and I thought I was “allergic” to the cold. It’s the exact same reaction but instead of sunlight it’s to the cold weather. Is it the same kind of treatment? What’s this exactly called? I have an appointment with a specialist in December. I’m just so intrigued by this because it seems to be the exact same thing it just happens when I go outside in the cold but it’s been getting better throughout the season.

  5. Thank You!! I thought I was the only one; at least one of the very few. Diagnosed at 30, now 49, my skin has not become more tolerant. May through August (in NY) are difficult to navigate; want to be outside covered in sunscreen, but it’s not enough. PLME and Roscea are a struggle.

  6. I get a similar looking rash from sun exposure that just started two summers ago (I’m 33). However, it only appears on my face even with other body parts exposed to sun. I wear SPF 50 (and reapply liberally) but the rash still appears 2 days after exposure and lasts for about 4-5 days. Is this likely a different diagnosis?

  7. I have suffered from PMLE for over 40 years. It has not subsided at all over the years. As I leave this comment today my hands are so swollen m, itchy, cramping and blistered from just a short time outside today. I even get it during the winter if the sun is shining through the car windows. My face also swells so bad that my eyes swell shut. People have no idea how painful this disease is and it never goes away and there’s is no cure.

  8. I got my first breakout when I was 8. Boy were kids mean about it. I have to avoid the sun as much as possible, even indirect sunlight or light that passes through windows will cause it. It also causes tiredness and itchy throat. It doesn’t always have to be a beautiful day either, it can look overcast and gray. It’s the uv index that matters, so if you have this too check the uv index daily for the area you live. /wave

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