Sunscreen: A Deep Dive
Updated: Nov 24, 2020
I've been meaning to write this post for a long time, but this is a HUGE topic and I wanted to be exhaustive. So buckle up, because it's going to be a long one!
Let's start with WHY we need to protect our skin from UV.
UV radiation from the sun, damages our skin cells. More specifically, it damages the DNA within our cells, causing mutations in the genetic code. These mutations create gaps in the genetic information required for our cells to divide into new healthy cells.
Over a lifetime of exposure, that damage is cumulative. It can (and will) have significant consequences for our health - and I'm not just talking aesthetics here, I'm talking about the health and function of your body's largest organ (making up around 16% of your total body mass).
Some possible consequences of a lifetime of unprotected UV exposure include: skin cancers such as basal cell carcinomas, squamous cell carcinomas, and malignant melanomas (which, let's not forget, can metastasise and develop into other cancers), skin atrophy or hypertrophy (excessive thinning or overgrowth), reduced ability for cellular repair resulting in slower wound healing, and reduced immune function leading to an increased likelihood of skin infections.
In terms of what you'll see in the mirror: telangiectasia formation (visible red blood vessels), thinning of the dermis (deeper layer of the skin) and/or excessive thickening of the outer layer of the skin, pigmentation ("age spots", freckles), formation of wrinkles and lines, overall dull or sallow complexion, enlarged pore size, and "sagging" or skin laxity. Your skin will look worse on the outside, because it is no longer functioning properly on in the inside.
The good news is, much of this damage is PREVENTABLE - if we only take the time to protect our skin properly.
Now let's talk about UV itself.
UV radiation is classified as a "complete carcinogen", because it is both a mutagen (able to alter your DNA and increase the likelihood of genetic mutations), a damaging agent, and it has the properties of both a tumor initiator, AND a tumor promoter. UV exposure is THE most important controllable risk factor for skin cancer.
There are three types of UV: UVA, UVB, and UVC. The types most relevant to us are UVA and UVB.
UVC is completely absorbed by the earths ozone layer, so our exposure to it on earth is limited - we can only really be exposed with the use of mercury lamps, welding torches and old school tanning beds.
UVB is only partially absorbed by the ozone layer, so we DO get exposure to it on earth. UVB (or "UVBurn" as I like to call it) is responsible for most sunburns, and is strongly linked to skin cancer development. Intensity of our exposure to UVB varies depending on time of day, season, and location in the world. Interestingly, damage from UVB actually takes time to become apparent. You might have noticed sunburns can take hours to fully develop - you can leave the beach looking fine, and only have your sunburn become visible a few hours later .
UVA accounts for around 90% of all of our UV exposure. It penetrates deeper than UVB, causing damage to the deeper layers of the skin. UVA is present to the same degree regardless of cloud cover, season, location, time of day (as long as the sun is still up), and is still causing DNA damage in your skin. This is the reason you still need to wear sunscreen on a cloudy day - as long as there's daylight, there's damage being done.
Now for the age old question: If I have darker skin, do I need to wear sunscreen?
The answer: darker skin IS at a much lower risk of developing skin cancer due to the UV protective qualities of the skin's higher melanin content. But that doesn't mean the skin cannot be damaged, particularly by UVA which penetrates into the deeper layers of the skin. Melanin provides some protection, but not complete protection.
Not only that, but darker skin is more prone to developing PIH (post-inflammatory hyperpigmentation), AKA the dark marks that are left behind after trauma to the skin, usually acne/breakouts. UV exposure increases the risk of developing PIH and can darken existing PIH.
The darkest human skin tones have a natural protection of around SPF13 - we recommend everybody wear sunscreen SPF30+, regardless of skin colour/tone.
CHEMICAL vs PHYSICAL - What does it mean?
Chemical sunscreens once applied, sit within the upper layer of the skin and absorb UV rays. There are a multitude of active ingredients that can make up a chemical sunscreen, including: oxybenzone, homosalate, octocrylene, avobenzone, and more. Chemical sunscreens do have a higher chance of causing irritation to the skin, some active ingredients more than others - but they also tend to have a lighter consistency than physical sunscreen, so can be better for oily/congested skins.
Physical sunscreens once applied, sit on top of the skin and reflect UV rays. There are only two active ingredients for use in physical sunscreens: Zinc Oxide and Titanium Dioxide. Physical sunscreens tend to be less likely to irritate - but can be a little heavier in consistency than their chemical counterparts.
Is SPF15 enough?
Not really. SPF30 or 50 is ideal. There's actually not a huge difference between SPF30 and SPF50 - read the guide below:
SPF15 - blocks around 93% of UVB rays
SPF30 - blocks around 97% of UVB rays
SPF50 - blocks around 98% of UBV rays