Should I still use sunscreen if I’m in the shade?

Potentially, yes. Ultraviolet (UV) light is scattered in the atmosphere. When you’re in the open, half the UV rays reaching your skin come directly from the Sun. The rest is scattered UV that comes from the sky. If you’re in shade, you’re still exposed to this scattered UV.


Why do I burn so easily at the seaside?

Lots of people think it’s because the UV is reflected off the water, but that’s not true. Very little comes from the sea.

The reason is that there’s no shade. You have this whole wide sky around you, so you’re receiving the UV from the Sun, and all the scattered UV from the sky.

Read more scientists' guides:

How should I apply sunscreen?

Sunscreen works by forming a barrier between the Sun’s rays and the living cells of your skin.

Don’t rub it in vigorously because that forces it deeper into the skin, and you end up exposing the vulnerable cells near the surface. You want it to rest on the surface of your skin, so spread it smoothly, then let it dry.

How much should I apply?

When manufacturers test the SPF (Sun protection factor) of their products, there’s an internationally agreed thickness of 2mg per centimetre of skin, but my research shows that people tend to put on roughly half this amount because otherwise it feels too thick.

So, if you use an SPF30 sunscreen, you end up with a delivered SPF of 10 to 15. The way round this is to put on a layer of sunscreen the way you like it, let it dry, then apply a second layer around 30 minutes later.

More like this
Need to know:
  1. Even if you’re sitting in the shade, you should still apply sunscreen.
  2. Expensive sunscreen doesn’t equal better protection.
  3. Don’t rub it in. You need a layer of Sun protection on top of your skin


How does suncream protect you from sunburn? © iStock

Should I apply sunscreen every day?

Some people say you should, but there’s no need.

In the winter, the Sun is weak, we stay inside more and we’re covered up. In the summer, if you’re just nipping outside for half an hour, it’s okay too.

Being overly concerned is detrimental. We all need a bit of sunshine to make vitamin D.

Are expensive sunscreens better than budget ones?

Not necessarily. You’re not paying for better protection. You’re paying for aesthetics. These products might smell or feel better, but it’s all down to individual preference.

I go for mid-range products made by reputable manufacturers.

What key ingredients should I be looking for?

A good sunscreen contains different ingredients, each designed to focus on a particular range of UV wavelengths.

Don’t worry about the specific ingredients. Instead, turn the bottle over and look at the star rating. This is something I invented. Four or five stars means you have protection against the whole UV spectrum.

Is high SPF better than low SPF?

Yes, in principle, but some products with higher SPFs are difficult to spread. They feel a bit claggy, so people tend to put less on. It’s important to balance the aesthetic qualities of sunscreen with the concentration of its ingredients.

  • This article was first published on BBC Science Focus in July 2019 – subscribe here


Follow Science Focus on Twitter, Facebook, Instagram and Flipboard


Helen Pilcher
Helen PilcherScience writer, presenter and performer.

Helen Pilcher is a tea-drinking, biscuit-nibbling science and comedy writer, with a PhD in cell biology.