A fourth heatwave has just got underway for much of the UK, with temperatures set to hit up to 35C, but with long spells of sunshine comes a higher risk of sunburn and skin cancer10:30, 29 Jul 2026A doctor has explained why she always wears suntan lotion inside - even on her commute and while sitting at her desk. A fourth heatwave has just got underway for much of the UK, with temperatures set to hit up to 35C today (July 29), with the highest temperatures focused on the Midlands and the south and east of England.‌And with long spells of sunshine comes a higher risk of sunburn and skin cancer, making it important to apply sun cream when you’re out and about. But it turns out it can matter indoors, too.‌Trisha Pasricha, MD, an instructor in medicine at Harvard Medical School in the US, shared the advice in a recent column, in which she responded to a query about the subject.‌She said the answer is we should indeed wear sun cream indoors, despite it seeming "counterintuitive".Trisha wrote for The Washington Post: "Why do people in the United States tend to get more skin cancers on their left side, while people in Australia appear to get more sun damage on the right? The answer is UVA exposure while driving."‌She noted that humans can only see visible light, not ultraviolet (UV) waves. But while standard glass in windows tends to block sunburn-causing UVB rays, it offers little protection from visible light or UVA.Trisha said the concern is that both visible light and UVA can accelerate skin ageing. She cited a 2011 study that analysed more than 82,000 melanoma cases, alongside about 2,400 Merkel cell carcinoma cases.It concluded that both types of cancer were somewhat more frequent on the left. Past studies also suggest that in Australia, where drivers sit on the right, pre-cancerous patches tend to appear more often on the right side.‌Trisha added: "So, yes, I do wear sunscreen every day despite working indoors. I commute at least 45 minutes to my office each way. I also face a nice, large window behind my computer screen when I’m there."So even though I don't actually step foot outside most of the day (tragically), my skin is getting UVA rays for much of my indoor time."‌The NHS states that sunburn raises your risk of skin cancer. It also stressed that sunburn is not limited to when you're on your holidays, as you can still get burnt in the UK - even when it's cloudy.It points out that there is "no safe or healthy way" to get a tan and suggests that we stay in the shade when the sun is at its strongest. If the UV index is 3 or higher, you should protect yourself.It also advises us not to get burnt, to cover our skin with appropriate clothing, wear sunglasses, and to take particular care with children and babies (keep babies out of direct sunlight if they're under 6 months).Article continues belowAs for sun cream, the health service says you should opt for at least factor 30, use enough and reapply it often.You can read more about sun safety on the NHS website.