Lloydspharmacy.com Health - Safe in the sun: what's in a sunscreen

Written by Dr Charlie Easmon, specialist adviser in travel medicine

We all enjoy the sun, but how we react to its rays varies from one individual to another.

The number of cases of skin cancer has doubled in the last 20 years.

The Australians launched a successful campaign: 'Slip,Slop,Slap', to reduce sun induced skin cancers, and it is a simple as: 'slip on a shirt, slop on sunscreen, and slap on a hat'. This often means that any one bright red on an Australian beach, is not Australian!

We need to constantly watch out for our skin in the sun. Some people - often those of us who have fair skin - need to take greater care than those who have slightly darker skin.

Why does skin tan?

We all have one thing in common: we tan from staying in the sun because our skin forms the substance melanin.

It's this substance that makes skin darker, and it's the skin's own sun protection.

We form melanin at differing rates, which is why some people tan faster than others and some don't tan at all.

People who produce the least melanin, ie those who burn easily, are at highest risk of skin cancer.

The effect of the sun's rays depends on where we are, how strong the radiation is and what type of skin we have. The sun is strongest the nearer we are to the equator.

How do sunscreens work?

Sunscreens work in different ways to protect us against the rays of the sun. They can have a chemical or physical sun filter or have a mixture of the two.

Sunscreen and allergy

People who have an allergic reaction to the ingredients of sunscreen are best off choosing a cream with a physical filter.

Chemical filters penetrate the skin and absorb the sun's rays so they don't reach down into the lower layers of skin and cause damage.
Physical filters lay a thin membrane on top of the skin that reflects the sun's rays back. A physical filter is often slightly coloured, such as zinc oxide which is white.

A sun lotion that protects against both ultraviolet type B (UVB) radiation and ultraviolet type A (UVA) radiation offers the best protection. These creams are called 'broad spectrum' sunscreens.

Some chemical filters only provide protection against the UVB radiation of the sun, while others protect against both UVB and UVA radiation.

Physical sun filters protect against both the UVB and UVA rays of the sun.

What's the difference between UVA and UVB rays?

UVB rays burn the topmost layer of skin, causing sunburn and cell damage that can lead to cancerous changes.

Sun protection factor (SPF) measures the strength of a cream's sun filter against UVB rays.

Sunscreens with a high SPF factor should not lead to you staying in the sun for longer, since you'll be exposed to more UVA rays.

UVA rays don't burn, but penetrate deep into the skin. They are responsible for cell damage that contributes to ageing and skin cancer.

UVA stars

Five stars gives 90 per cent of the UVB protection.

Four stars is 80 per cent.

Three stars gives 60 per cent.

Two stars is 40 per cent.

One star is 20 per cent.

UVA stars indicate the strength of a cream's protection against UVA rays in relation to its UVB protection.

This means the higher the SPF, the more UVA protection is needed to achieve the same amount of stars.

So an SPF 30 sunscreen with three stars will have more UVA protection than an SPF 15 sunscreen with four stars.

What factor should I choose?

The SPF you need depends on your skin type.

Most of us can manage with an SPF 15, and it doesn't make much of a difference if you go for higher factor numbers.

Exceptions are adults who tend to get eczema and children. In these cases, an SPF 25 or higher is recommended.

It is a good idea to use a stick applicator with a higher SPF for particularly exposed areas of the body such as the shoulders, nose, lips and ear lobes.

The sunscreen should also have at least four UVA stars.

Even the highest SPF broad spectrum sunscreen cannot fully protect against UVA and UVB rays. This is why people should cover up and stay in the shade at the hottest times of the day (11am-3pm).

A good tip here is to avoid going into direct sunlight when your shadow is shorter than you are.

Waterproof or water-repellent?

If you like to go for a swim to cool down, you need to make sure that your sun lotion is either water-repellent or waterproof.

A waterproof sunscreen withstands 4 x 20 minutes of swimming without being washed off.
A water-repellent sunscreen withstands 2 x 20 minutes without being washed off.

These figures only apply if you let yourself air-dry and don't use a towel. It is therefore always a good idea to rub on a layer of cream after going for a dip.

Are there any tips for application?

Apply cream thickly and often: many people use only a third of the amount of cream they need to achieve the SPF on the bottle. This means they are far less protected than they think.

An adult should apply a handful of sun cream, equivalent to 30 to 40g. This equals about two tablespoons.
A child needs about 20g to cover the whole body.

Sun lotion takes time to work, so you need to apply cream half an hour before going out into the sun.

Children should also be covered with light clothing, while babies under 12 months should not stay in the sun at all.

Can I use sun lotion left over from last year?

Not with safety. Sunscreens have a shelf-life of more than two and a half years. This means the manufacturer is not obliged by law to quote an expiry date.

But both heat and bacteria damage sunscreens, so you should replace your lotion each year.

If your sunscreen smells off or separates, it is either full of bacteria or has been destroyed in some other way and should be thrown out.

Keep sun lotion in a shady and cool place when not in use, ideally in the refrigerator.

Last updated 20.08.2009