An itchy red rash that appears after you've been in the sunshine can come as a surprise – and plenty of people experience it. Although it's often written off as prickly heat, it may actually be a reaction to something else. And if you're taking certain medicines, including atorvastatin or naproxen, it's sensible to check in with a GP.
Well-known TV doctor Dr Mark Porter raised the issue after hearing from someone who suspected prickly heat and said friends had encouraged them to skip sunscreen. In his view, the pattern of symptoms was more consistent with polymorphic light eruption (PLE) than with heat rash.
What is polymorphic light eruption?
In a blog post on SAGA, the NHS GP explained that prickly heat is due to blocked sweat glands. He said it was more often seen in hot, humid conditions. He said it is often confused with prickly heat.
He said: "PLE is a sensitivity to sunlight, mainly the highly penetrative UVA component that can pass through clouds, water, glass and even some clothing. It causes an itchy, red rash that develops anywhere from a few hours to a few days after exposure, and the classic story is someone who notices it on the second or third day of their holiday in the sun."
Dr Porter, a doctor with almost four decades of NHS experience who was awarded an MBE for services to medicine in 2005, said PLE typically shows up on both sides of the body. He added that it most commonly affects areas such as the chest, arms and the tops of the feet.
Prevention and medication advice
The doctor said the main way to prevent it is to cut down on UVA exposure by using a high-quality sunscreen, ideally SPF 50 with a five-star UVA rating. You should reapply it every two hours. He also advised staying out of direct sunlight during the peak hours, typically between 11am and 3pm.
The medical expert stressed: "In new cases, it's worth checking whether recently started medications (such as some statins, doxycycline, thiazide diuretics or naproxen) could be triggering photosensitivity and discussing the rash with a GP."
He said some dermatologists recommend beta-carotene supplements, but cautioned that the evidence behind them is limited, calling the science "shaky." If someone chooses to try them, he noted the usual approach is about 15mg a day, starting a week before a sunny holiday and continuing until you're back – or taking them during warmer, sunnier periods at home.
Who is most at risk?
Because PLE typically starts in early adulthood – most commonly in women in their 20s and 30s – it would be less common for someone to develop it for the first time later in life. Dr Porter added that while certain medicines could potentially bring it on or make it worse, that isn't guaranteed. Anyone concerned about symptoms should seek advice from their GP.
Signs and symptoms of polymorphic light eruption
The NHS notes that the rash may:
- be itchy or feel like it's burning
- be red or pink – this may be harder to see on brown or black skin
- have larger blotchy areas
- have small raised spots or blisters
It adds: "The rash can appear anywhere on the body, but is often in places that are not regularly exposed to the sun, such as the arms, legs or chest. A similar type of rash on the ears can cause small blisters that may be itchy or uncomfortable. This is called juvenile spring eruption."
