Plagued by a summer rash? How to tell if it’s heat rash or something more sinister

SOARING temperatures are enjoyable until it can be uncomfortable, with heat rash a very common problem.

There are other rashes that flare up in the summer, some of which need more serious treatment.

The NHS says the three main symptoms of heat rash, in both adults and children, are:

  • Small, raised spots
  • An itchy, prickly feeling
  • Mild swelling

Heat rash is when sweat glands in the skin get blocked as a result of excessive sweating.

Babies are particularly at risk because they cannot control their temperature, and sweat more.

Usually a pharmacist will prescribe a calming lotion, a topical steroid cream or antihistamines.

During the British summer time, people will be spending more outdoors having picnics, dining al fresco or enjoying the beach.

Dr Philippa Kaye, a GP and author, wrote in the Mail on Sunday: “Up to one in four of the population suffers a diagnosable skin condition, and many of these are linked to sun exposure.

“Indeed, in the summer months I see a raft of rashes and other skin complaints in my surgery that are far less common during the winter.

“Alongside heat, which causes problems in itself, the sun emits invisible ultraviolet (UV) radiation.”

UV rays can cause a number of rashes, as well as skin ageing and skin cancer.

Here are some sinister rashes to look out for:

Polymorphic light eruption

Polymorphic light eruption is a nasty rash that can be mistaken for prickly heat.

It often doesn’t show up for two to three days after being in the sun, and can take two weeks to heal.

The symptoms are:

  • Patches of 2mm to 5mm pink or red raised spots
  • Some people get blisters that turn into larger, dry, red patches – it looks a bit like eczema
  • Less commonly, the skin patches look like targets or bull's eyes

Sometimes as little as 30 minutes of sun exposure is enough to cause this rash, the NHS says.

And it can even develop through thin clothing or if you're sitting near a window.

Dr Kaye said: “Polymorphic light eruption affects between one in ten and one in 20 people, and women account for roughly three-quarters of all sufferers.

“It can run in families, and typically it's seen in those with fair skin, but people with darker skin can get it too.

“It's thought to be due to an immune-system reaction, and the first episode usually happens between the ages of 20 and 40.”

Sadly there's no cure for polymorphic light eruption but there are many ways to try and ease the symptoms or prevent it from happening.

This includes suncream, vitamin D supplements and desensitising – when you sit in the sun for periods of time during the spring to toughen the skin.


Phytophotodermatitis happens when sunlight reacts with plant compounds.

These include foods like figs, citrus fruits, carrots and celery.

Dr Kaye said: “Gardeners can get it on their hands – giant hogweed is a common cause, as is rhubarb.

“Citrus fruits can also trigger the reaction, which is why we often see it round the mouths of children who have been eating ice lollies made with real limes or lemons.”

Bartenders, food handlers and grocery workers may also be affected if they work in the sunshine.

Sometimes people have no idea what has caused their rash because they may not recollect coming into contact with the substance.

It also goes by the name of “margarita rash” because the cocktail, made using limes, could lead to blistering around the lips.

The rash can come up within 24 hours of exposure, but last several weeks.

The rash causes:

  • Blister-like patches at the start that are irregularly shaped (sometimes in the same pattern as where the substance touched the skin, such as drips)
  • Redness
  • Swelling
  • Pigmentation that can last several months after healing

Jock itch

Jock itch is a fungal infection that is more common in humid temepratures.

It starts when bacteria grow in a damp, close environment.

The rash is typically seen in the groin area and often in athletes.

And the fungus can be passed between people through items like towels – similar to athlete's foot.

Those most at risk include men, people who are young, sweat heavily, have a weaker immune system or diabetes.

The rash starts as a reddened area of skin in the crease in the groin and may spread to the upper thigh in a half-moon shape.

Symptoms include:

  • Burning
  • Itching
  • Skin that becomes flaky or scaly
  • Redness
  • Rash that gets worse with exercise or activity
  • Changes in skin colour
  • Doesn’t improve with steroid creams

Although a “fungal infection” may make your skin crawl, jock itch is quite mild.

Most people find that topical antifungal medicines, and keeping the area dry and clean, help it to go away.

“Showering or washing daily, drying off thoroughly and getting out of damp clothes quickly are the best forms of prevention,” Dr Kaye said.

Insect bites or stings

When the weather heats up, the bugs come out.

Insect bites and stings will usually cause a red, swollen lump to develop on the skin. This may be painful and in some cases can be very itchy.

It usually goes away within a few hours or days.

But some people will have an allergic reaction, either causing mild symptoms such as swelling, or severe symptoms.

Dr Kaye told The Sun: “Anaphylaxis from a wasp sting would be an emergency.”

Symptoms of a severe allergic reaction include:

  • Breathing difficulties
  • Dizziness
  • Swollen face or mouth
  • Feeling sick or being sick
  • A fast heart rate
  • Difficulty swallowing
  • Loss of consciousness

Swimmer's itch

Cercarial dermatitis also known as swimmer's itch, is an allergic reaction to parasites.

If you've been swimming in lakes, rivers or the sea then these parasites may have burrowed in your skin, causing a red itchy rash and even blisters in some cases.

Usually you will experience a tingling immediately after swimming and in 12 hours this will turn into small red pimples.

One per cent hydrocortisone cream is sold over the counter and will help get rid of the rash.

Most rashes will clear up within a week but if it becomes uncomfortable you can always use a cold compress.

Symptoms, that appear between minutes or days after swimming in infected waters,include:

  • Tingling, burning, or itching of the skin
  • Small reddish pimples
  • Small blisters

When to go to A&E or call NHS 111

The American Academy of Dermatology Association says the following are signs you need to seek medical attention:

  1. The rash is all over your body. A rash that covers the body could indicate something concerning, such as an infection or allergic reaction.
  2. You have a fever with the rash. This could be caused by an allergic reaction or an infection. Examples of rashes caused by infection include scarlet fever, measles, mononucleosis, and shingles.
  3. The rash is sudden and spreads rapidly. This could be the result of an allergy. Allergies to medications are common, and some can be serious. If breathing becomes difficult, call 999.
  4. The rash begins to blister. If your rash is made up of blisters, or if the rash turns into open sores, it could be the result of an allergic reaction, a reaction to medication, or an internal cause. Seek medical attention if a blistering rash affects the skin around your eyes, multiple areas in your mouth, or your genitals.
  5. The rash is painful. Painful rashes should quickly be evaluated by a doctor.
  6. The rash is infected. If you have an itchy rash and you scratch it, it may become infected. Signs of an infected rash are yellow or green fluid, swelling, crusting, pain, and warmth in the area of the rash, or a red streak coming from the rash.

Solar urticaria

Urticaria is a condition the leads to itchy hives, weals or nettle rash.

Some people's urticcaria is triggered by exposure to sunlight, as well as the cold, wind, water, food, medicine, sweat and plants.

The sun causes cells in the skin to release histamine, causing a rash within minutes, according to the British Association of Dermatologists.

The main symptoms of solar urticaria are:

  • Flat red marks or raised red/white weals on the skin
  • Itching, stinging or burning skin
  • Rarely the rash is accompanied by symptoms such as headache, nausea, vomiting, breathing difficulties and low blood pressure.

Urticaria is difficult to treat and becomes a lifelong problem for most sufferers.

It involves avoiding the source of the condition – those with solar urticaria need to stay in the shade, cover themselves in clothes and suncream and sometimes take medication.


Itchy skin, in rare circumstances, can be a sign of cancer.

For example one in three people with Hodgkin lymphoma get itchy skin, which feels a bit like heat rash.

Leukemias and lymphomas, gallbladder cancer, pancreatic and liver cancer also cause itchy skin, sometimes as a result of build-up of bile salts or substances secreted by a tumour.

Itchy skin could also be a sign of skin cancer if it comes with a new skin growth, change in mole, a sore that won't heal, rough or scaly skin patch or pink bump that bleeds easily.

Xeroderma pigmentosum

Xeroderma pigmentosum (XP) is a very rare inherited skin disorder where the person is extra sensitive to the DNA damaging effects of UV.

Dr Kaye said even light bulbs can exacerbate the condition.

She told The Sun: “About half of patients will have blistering type burns after even a small amount of sun exposure but the other half won't.”

The half that don’t get blistering burns in the sun get a tan.

But both types of reactions also result in lentigos (freckling) of the skin the appear before the age of two years old.

People are usually diagnosed by the age of two years old.

They may have severe sunburn after their first time in the sun.

Symptoms of XP include:

  • Blistering burns on exposed skin, sometimes after less than 10 minutes in the sun, typically of the skin, eyelids and tip of the tongue.
  • Thin skin
  • Pigmentation
  • Red lines and patterns on the skin caused by widened blood vessels
  • Dry skin and eyes
  • The eyelids and the surface of the eyes will usually be affected within the first decade of life
  • Hearing loss
  • Progessive mental impairment

Dr Kaye said: “[It] causes premature skin ageing and increased risk of skin cancers.”

People with XP have a 10,000-fold increased risk for developing skin cancer, according to the National Organization for Rare Disorders.

They also have a 2,000-fold increased risk for cancer of the eye and surrounding tissues.

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