Sunlight generates free radicals that damage the skin

A couple of people have picked up on something from my review of Aldi’s Anti-wrinkle cream. This has an SPF of 4, which I thought was about right for a day cream. Shouldn’t I be suggesting at least SPF15 they ask. I don’t think I should: I think it is about right. But I do see why people might not agree with me so I thought I would lay out my thinking on sunscreens and healthy skin in a bit of detail.

I think everyone by now must know that sunlight ages your skin. It also increases your risk of skin cancer. In countries like Australia which has a population living in much stronger sunlight than where it originated, skin cancer rates are very high. It is even possible to link this effect to different levels of sunlight. The rate of skin cancer in Australia is higher in the regions that get most sun.

We have a pretty good idea of what is going on in the skin when sunlight shines directly on it. The ultraviolet radiation can break down oxygen molecules to produce highly reactive free radicals. These free radicals will damage just about anything they come into contact with. The skin’s tightness comes mainly from a long protein molecule called collagen, and this can broken down by free radicals.

The skin has a battery of defense mechanisms against these free radicals, but the most important one is simply rebuilding molecules damaged by the free radicals. Every second of the day our skin is working to repair the damage that these free radicals are doing. Another defense mechanism in the skin are anti-oxidants that simply absorb the free radicals. The best known of these is vitamin E. It is also worth remembering that most processes involved with this defense are water based. They will work better in well moisturised skin in good condition.

At the end of the day it is a numbers game. Can the free radicals break down the skin’s defenses quicker than the skin can rebuild them. Northern Europeans have evolved the defenses they need to cope with Northern European sun levels. Move them to Australia or even Southern France and they are vulnerable.

One thing we can do to help our body in its continual struggle with free radicals is to help block out the sunlight by using a cream with an SPF (Sun Protection Factor). The SPF is calculated by how much longer it takes for the skin to burn in bright sunlight when you apply the product. So if you are wearing an SPF10 cream, you can stay out in the sun for 10 hours if you would normally burn in an hour. This is a useful way to judge how effective different creams are compared to one another. But I don’t think you can say that you should necessarily use the highest and that this will be best.

The way a chemical sunscreen works is that it absorbs high energy UV radiation and re-emits at a lower less harmful level. The fact that the molecule is absorbing the light inevitably means that it will be broken down. So as soon as you apply a chemical sunscreen it starts to lose its effectiveness. Your SPF 10 cream is going to steadily decrease in effectiveness as it remains exposed to sunlight. I suppose it could be argued that starting with a big number will give you more protection for longer. But to my mind you are better off applying a lower SPF cream more often.

I am also not convinced that it is a good idea to put a lot of chemical sunscreen on the skin. Let me make it clear right away that I am not one of those people who thinks that chemical=bad. I am a chemist. Chemicals are my friends. At the end of the day everything is a chemical. But just like there are people you like and people you trust, and people you are a bit more ambivalent about, I don’t like all chemicals equally. See my post on vanillin for one of my friends. Chemical sunscreens are a crowd I am a bit suspicious of. I know that they have all been tested for safety and have well known toxicological profiles, but nonetheless I am not keen on them. I think it is the way they break down after they have been absorbed into the skin.

On top of that, I am also bothered by the shapes of the molecules.

This is the shape of octyl methoxycinnamate. It might not mean much to you, so you will have to trust me on this. The barrier function of the outer layer of the skin relies on a very clever plate like structure. This structure can be disrupted by materials that have the wrong shape. Sodium lauryl sulphate,SLS, is one such which is why it it drys the skin out. I have a feeling that most of the chemical sunscreens are also likely to have a disruptive effect. You may not notice it because they are also very oily, but I think that they might have a long term drying effect on the skin. This is not only a bad thing in itself, but might well hinder the skin’s own protective mechanisms.

I much prefer physical sunscreens. These are pigments that sit on the surface of the skin and reflect the light. They aren’t absorbed and they don’t break down. You will lose protection as they brush off the skin but they won’t leave any breakdown products in your skin. The problems with them is that because they literally reflect the light falling on the skin back, if you use high levels they make you look paler. If you want a high SPF using physical sunscreens you tend to end up looking a bit ghost-like. The names to look for on the ingredient list are titanium dioxide and zinc oxide.

The sad thing is I think the trend for higher and higher SPF values has stopped the more widespread use of physical sunscreens. If you need to beat SPF15 you are really going to struggle to come up with a good physical sunscreen formulation.

The ironic thing is I don’t think that overall high SPF formulations make much contribution to protecting yourself from the sun. If you really need a high level protection – say you are very fair skinned and have to be in the sun for a prolonged period of time – you always have the option of just using more of a low SPF cream. In any case I don’t think that just blocking the sun is the whole story. The skin has a very good defense mechanism already in place. One way of making sure it works effectively is to keep the skin well moisturised. I can’t produce a trial to prove it, but I believe that a low SPF cream that was also a good moisturiser and which didn’t contain anything to disrupt the skin’s barrier would be a more effective sunscreen than a high SPF formulation based on less skin friendly ingredients. And if you are after the very high SPF values that we see on chemist’s shelves a lot nowadays, you don’t have much of a chance to make it a good moisturiser.

I was intrigued to read a posting on the Money Saving Expert website where a woman stayed out in the sun but only got burned on the parts of her body where she hadn’t used her moisturiser!

So this is my tip for optimum antiageing protection for your skin. Find a cream with some sun protection but make sure it is a good moisturiser. Don’t look for a particular number. If possible it should use titanium and/or zinc oxide as the only sunscreen agents. Use it often. The Aldi cream wouldn’t be my ideal but it is the best one I can name at the moment. And see how it goes-we are all different so you need to find what works for you.

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