When it comes to sun protection, two arguments have been getting a lot of air time. First, that we should be slapping on SPF (sun protection factor) every day – even in winter – lest we end up looking haggard. Second, wearing SPF even on days when there’s very little sun puts us at risk of vitamin D deficiency. Which is right?

Neither, says Prof Helen MacDonald of the University of Aberdeen, an expert in sunlight and health. “SPF only stops UVB [radiation],” she says, explaining that although this wavelength both increases the risk of burning and skin cancer and is used by our bodies to produce vitamin D, it doesn’t cause the skin damage that leads to signs of ageing – that’s longer-wavelength UVA radiation. In order to block UVA, you need a broad spectrum sunscreen, one with a four- or five-star UVA rating. A moisturiser that just says “SPF 30” and nothing else on the packet is unlikely to work.

Another difference between UVA and UVB? In the UK the sun is so low in the sky in winter that most UVB rays get lost in the atmosphere. (April to the end of September is the period for making vitamin D; the lowest risk of sunburn is from mid-October to mid-March.) UVA is present year-round though, as “it’s not affected to the same extent by weather, where you live or the season”, says MacDonald.

So it is worth protecting yourself from it by using a broad spectrum sunscreen in the winter as well as the summer – and doing so won’t decrease the amount of vitamin D Brits make from sunlight in the winter because we don’t synthesise it at this time of year anyway.

How do we make sure we’re making enough vitamin D? Skip sunscreen when you’re going outside for 10 minutes or less in the summer and use supplements in the winter.