Are Smaller Amounts Of Sunlight Dangerous To The Skin At All?

As we enter into less-sunny days in the N. Hemisphere, do we still need to worry about the sun, or can we pretty much forget about it for 6 months?

Total UV of the sun

Rsearchers (Dr. Rachel Neale et al.) investigated exactly this matter, and found that total UV dose matters, and more specifically, that the same total dose of UV radiation can cause similar skin damage whether it is received quickly during stronger sunlight or more slowly during weaker sunlight.

However, you can’t just go off the cues that many people depend on to know if the sun is a problem, as for example DNA damage can occur without redness; in the study, participants with light to olive skin developed measurable UV-induced DNA damage, even when exposure was too low to make their skin visibly pink.

Further, Dr. Neale and her team found protein markers and UV-induced DNA lesions, indicating that skin cells were responding to DNA damage before any cancer had developed.

When we say “total UV dose matters”, we don’t just mean “at once”, but rather also that cumulative exposure adds up, insofar as repeated small amounts of incidental UV exposure over months and years can accumulate, causing mutations that can contribute to the development of skin cancer.

In practical terms, this means that indeed weaker sunlight isn’t necessarily risk-free, and spending longer outdoors during periods of lower UV intensity can still contribute to skin damage, so the researchers recommend using sun protection during everyday periods of exposure, particularly when the UV index is 3 or higher (if you look on your phone’s weather app, it will usually give a UV index number).

You can find the paper itself, here: The burning question: Does exposure to low dose and low irradiance ultraviolet radiation lead to cutaneous DNA damage in people with skin types I–III?

How this happens

The reason it is advisable to wear sunscreen in less sunny weather is (as illustrated by the above results) not generally about sunburn, and is rather more about long-term cumulative skin damage (ranging from accelerated aging to cancer) caused by the UV rays—specifically, mostly UVA rays, since UVB rays (with their higher energy but shorter wavelength) have nearly all been blocked by the atmosphere.

Here’s a good explainer of that from the American Cancer Society:

UV (Ultraviolet) Radiation and Cancer Risk

👆 this may seem like a no-brainer, but there’s a lot explained here that demystifies a lot of things, covering ionizing vs non-ionizing radiation, x-rays and gamma-rays, the very different kinds of cancer caused by different things, and what things are dangerous vs which there’s no need to worry about (so far as best current science can say, at least).

Consequently: yes, if you value your skin health and avoidance of cancer, wearing sunscreen when out even in the winter is a good idea. Especially if your phone’s weather app says the UV index is “moderate” or above, but even if it’s “low”, it doesn’t hurt to include it as part of your skincare routine.

But what if sunscreens are dangerous?

Firstly, not all sunscreens are created equal:

Learn more: Who Screens The Sunscreens?

Secondly: consider putting on a protective layer of moisturizer first, and then the sunscreen on top. Bear in mind, this is winter we’re talking about, so you’re probably not going out in a bikini, so this is likely a face-neck-hands job and you’re done.

What about vitamin D?

Humans evolved to have more or less melanin in our skin depending on where we lived, and white people evolved to wring the most vitamin D possible out of the meagre sun far from the equator. Black people’s greater melanin, on the other hand, offers some initial protection against the sun (but any resultant skin cancer is then more dangerous than it would be for white people if it does occur, so please do use sunscreen whatever your skintone).

Nowadays many people live in many places which may or may not be the places we evolved for, and so we have to take that into account when it comes to sun exposure.

Here’s a deeper dive into that, for those who want to learn:

The Sun Exposure Dilemma

Take care!