Heat Rash vs Sun Poisoning: What’s the difference?

Spending time in the sun is one of the best parts of summer, but it can also bring some unwelcome skin reactions. Two of the most common are heat rash and sun poisoning. They can look similar, and both tend to appear during a holiday or a heatwave, but they have different causes and require different treatments.

Heat Rash vs Sun Poisoning: At a Glance

	Heat Rash	Sun Poisoning (PLE)
Cause	Blocked pores trap sweat under the skin	Overexposure to UV light
Who gets it	Anyone, especially in humid weather	People with fair skin or sun sensitivity
When it appears	During or after sweating heavily	Hours after sun exposure
Common symptoms	Small red bumps, prickling or stinging, itching	Itchy skin rash, blisters, swelling
Location	Skin folds, areas covered by clothing	Exposed areas: arms, chest, neck
Treatment	Cool the skin, calamine lotion, hydrocortisone cream, antihistamines	Stay out of the sun, take antihistamines, use steroid cream
Needs a doctor?	Not usually needed, but over-the-counter treatments can help	Sometimes, if severe

What is heat rash?

Heat rash (also called prickly heat or miliaria) is a type of rash that happens when blocked pores trap sweat under the skin. Instead of evaporating normally, it gets trapped, causing irritation and a characteristic bumpy rash.

It is most common in hot, humid weather and tends to affect areas where sweat collects or where clothing rubs. Heat rash is common in babies and young children, but it can affect anyone during a heatwave or in a hot climate.

Despite the name, heat rash is not caused by the sun directly. It is caused by sweating, which is why it often appears in skin folds and under clothing rather than on exposed skin.

What does a heat rash look like?

Heat rash usually appears as small, raised bumps or blisters on the skin. They are often red, though on darker skin tones they can be harder to spot and may look more skin-coloured or brown.

The rash tends to appear in clusters and is commonly found on the neck, shoulders, chest, groin, and under the arms. In babies, it often shows up on the face, neck, and nappy area.

Source: NHS

What are the symptoms of heat rash?

The most common symptoms of heat rash are:

• Small red or pink bumps on the skin
• A prickling or stinging sensation, often described as feeling like pins and needles
• Itching, which can range from mild to quite intense
• Mild swelling around the affected area
• Skin that feels irritated or tender to touch

In most cases, heat rash is uncomfortable rather than serious. The rash usually goes away on its own within a few days once the skin cools down and stays dry.

If you notice signs of heat exhaustion as well as your rash, like dizziness, heavy sweating, or feeling faint, move to a cool place immediately and drink water. Heat stroke is more serious  and requires emergency medical attention.

In rare cases, heat rash can become infected if the skin is broken from scratching. Signs of infection include increased redness, swelling, pain, or pus. If this happens, it is worth speaking to a pharmacist or GP.

How can I treat a heat rash?

Heat rash usually clears up on its own, but there are things you can do to ease the discomfort:

• Move to a cool environment, or use a fan or air conditioning to lower your body temperature
• Remove or loosen clothing to allow the skin to breathe
• Apply a cool, damp cloth to the affected area for relief
• Take a cool (not cold) shower or bath and pat the skin dry gently
• Use calamine lotion or hydrocortisone cream to reduce itching and irritation
• Keep the skin dry and avoid heavy moisturisers or thick creams, which can block pores further
• Drinking plenty of water will help to regulate your body temperature and support recovery

Try to avoid scratching, as this can break the skin and increase the risk of infection.

You don’t usually need to see a doctor for heat rash, but speak to a pharmacist if the rash is not improving after a few days, is spreading, or if you notice any signs of infection.

What is sun poisoning (Polymorphic Light Eruption)?

Despite the dramatic name, sun poisoning is not actually poisoning. The medical term is Polymorphic Light Eruption (PLE), an allergic reaction to ultraviolet (UV) light.

Sunburn and sun poisoning are often confused, but sunburn is skin damage from UV exposure, while PLE is an immune reaction that can cause a rash even without burning.

When UV rays hit the skin, they can trigger an immune response in some people that leads to a sun rash. It’s one of the most common sun-related skin conditions in the UK, affecting an estimated 10-20% of the population.

PLE tends to happen more in the spring and early summer, when the skin hasn’t adapted to stronger sunlight yet after the winter months. People with fair skin or sun sensitivity are more likely to be affected, though it can happen to people with any skin type.

Unlike heat rash, sun poisoning has nothing to do with sweating or temperature. You can develop it on a cool, bright day just as easily as on a hot one. The trigger is overexposure to UV, not heat.

What does a sun poisoning rash look like?

The appearance of a PLE rash can vary quite a bit from person to person, which is reflected in the word “polymorphic” in its name. It can look different depending on your skin type and how severely you have been affected.

Common appearances include:

• Small red bumps or raised patches
• Blisters or fluid-filled spots
• Red, inflamed skin that looks similar to eczema
• Patches of dense, itchy bumps clustered together

The rash almost always appears on areas of skin that have been exposed to the sun, such as the forearms, backs of the hands, chest, and neck. Areas that are usually covered by clothing tend to be unaffected.

Source: NHS

Sun Poisoning Symptoms

Symptoms of PLE typically develop within a few hours of sun exposure, though they can sometimes take a day or two to appear. They usually last for several days before fading on their own.

The most common symptoms are:

• An itchy skin rash on sun-exposed areas
• Redness and swelling
• Small blisters or raised bumps
• A burning or stinging sensation
• Skin that feels sensitive or sore to touch

In more severe cases, some people also experience dehydration, headaches, nausea, or a general feeling of being unwell. If you develop a high fever, severe blistering, or feel very ill after sun exposure, seek medical attention promptly.

Symptoms tend to improve once you avoid the sun and give your skin time to recover. A lot of people find that their skin becomes less reactive as the summer progresses, as repeated sun exposure can desensitise the immune response over time.

How can I treat sun poisoning?

The most important first step is to get out of the sun and keep the affected skin covered. Beyond that, treatment focuses on relieving symptoms while the skin recovers.

• Take an antihistamine to reduce itching and calm the immune response
• Apply a mild steroid cream, such as 1% hydrocortisone, to ease redness and inflammation
• Use a gentle, fragrance-free moisturiser to soothe the skin
• Take paracetamol or ibuprofen if the skin is painful or you feel generally unwell
• Stay out of the sun until the rash has fully cleared

Don’t apply perfumed products, exfoliants, or anything that could further irritate the skin while it is reacting.

If you get PLE regularly, it is worth speaking to your GP or a pharmacist. In some cases, a short course of prescription steroid cream may be recommended, or your doctor may suggest phototherapy, where the skin is gradually exposed to controlled amounts of UV light to reduce its sensitivity over time.

Preventing Summer Skin Problems

A few simple habits can go a long way in reducing your chances of developing either condition.

To prevent heat rash:

• Wear loose, lightweight, breathable clothing in hot weather
• Avoid exercising or being active during the hottest part of the day
• Take cool showers after sweating and dry the skin thoroughly
• Keep sleeping areas cool and well-ventilated
• Avoid heavy, oil-based creams and lotions that can block pores

To protect your skin from sun poisoning:

• Apply a broad-spectrum sunscreen with a high sun protection factor (SPF) to all exposed skin 15 to 30 minutes before going outside, and reapply every 2 hours
• UV rays are strongest between 10 am and 4 pm, so cover up or stay in the shade during those hours
• Cover up with loose clothing, a wide-brimmed hat, and sunglasses
• Build up sun exposure gradually at the start of summer if your skin tends to react
• Bear in mind that sunburn can cause a rash in its own right, and repeated sunburn increases the risk of skin cancer over time

If you are prone to PLE, a high-factor sunscreen formulated for sensitive or reactive skin can make a real difference.

Look After Your Skin With Click2Pharmacy

If you’re dealing with an uncomfortable heat rash or a recurring reaction to the sun, getting the right treatment quickly makes a difference. At Click2Pharmacy, you can order treatments for heat rash, including antihistamines, topical emollients and sun care products online, with fast, discreet delivery straight to your door.