There is no doubt about it. The biggest thing that makes your skin look old is sunlight. There is plenty of academic backup for this suggestion, but most of us can prove it simply by looking at ourselves. Areas of skin that are routinely exposed to light always look older than parts that don’t. In my case I have the habit of rolling my sleeves up in summer and the skin just below the join is rougher, darker and more hairy than above.
So it is good advice to use a sunscreen, particularly on your face. This is something that almost nobody disagrees with. Another aspect of this that is less commonly spoken about but is equally uncontroversial is that moisturisers can also help with sun protection. The skin has sets of enzymes that battle against the effects of sun damage and these work much better in well hydrated skin. So the ideal anti-aging solution is a moisturiser which also contains a sunscreen.
The obvious implication of all this is that this moisturiser should have a high SPF value. It stands to reason. Or does it?
I often surprise people who ask me by saying that I think a low SPF is actually better. My reasoning is simple. The sunscreen agents themselves are difficult to incorporate into moisturisers, and the more you put in the less elegant the moisturiser is. This makes it unpleasant to use. And if you don’t like using it you will use it less often.
It is worth remembering what an SPF value actually means. An SPF of 5 means you can stay out in the sun five times longer without burning than you would without the sunscreen on. My skin is so white that if I dose off in the office and don’t move I risk being mistaken for a ream of paper and inserted into the photocopier. But even I find that quite low SPF formulations give me pretty effective protection from sun burn.
The law of diminishing returns sets in pretty quickly with SPF values as well. An SPF 15 sunscreen blocks 93 percent of UVB radiation, while an SPF 30 sunscreen blocks nearly 97 percent. So you aren’t getting much extra protection for all that extra SPF.
You are also getting a formulation that is much less pleasant to use. I’d much rather use a low SPF cream more often. When SPF values are determined there is a set protocol that has to be followed. This is necessary because the whole point is for different products to be compared to one another. This means that an SPF 15 cream is better than an SPF cream when you use the same amount. The test doesn’t tell you what happens when you simply use more of the SPF 5 cream. But the relationship between the thickness of a film and its absorbance has been studied. (It’s the Beer Lambert Law if you want to look it up.) And so we know that this is one of those cases where common sense actually works. The more you use the more protection you get and using double the amount will roughly double the protection.
I also had a hunch that high SPF values lead to poorer moisturising performance. In fact I was pretty confident that this was the case. I have just never gone to the trouble or expense of actually proving it. But in the most recent International Journal of Cosmetic Science a couple of Brazilian researchers have investigated just this issue. Their conclusion was “The presence of sunscreens had a negative influence on immediate skin hydration and TEWL” To be scrupulously fair they did find that UV filters had some positives as well. But to my mind, moisturisation is the key thing you want.
So to conclude, I suggest that the optimum anti-aging approach is to use a low SPF moisturiser, but apply it frequently. This will keep your sunscreen levels up and also make sure you get the best moisturisation at the same time, which will help your skin do the best job it can of protecting against the effects of UV.
Int J Cosmet Sci. 2017 Dec;39(6):622-628. doi: 10.1111/ics.12424. Epub 2017 Oct 13.
Influence of UV filters on the texture profile and efficacy of a cosmetic formulation.
Fossa Shirata MM, Campos PMBGM.