How and when should a sunscreen be applied to the skin for the best protection from damage by sun exposure.

How

Most "directions for use" on sunscreen containers and packaging recommend that users "apply liberally" or "generously". While such directions might be considered rather vague, if the objective: to cover the exposed skin surface is remembered then it does become more intuitively useful. The skin needs to be well covered but only lightly rubbed in. Especially with sunscreens containing inorganic UV absorbers, reflectors, and scatterers like titanium dioxide and zinc oxide, do not rub them in too hard, they work best on the surface of the skin. The technology available for these UV – Filters enables them to be formulated in very tiny particles (micronisation) which may leave the surface of the skin with a milky glaze. This is quite useful for gauging which skin areas you are covering, and where you have missed.

If you do not spread enough sunscreen over the skin then you will not be protected according to the label claimed SPF (see below). Half as much will result in half the protection.

The outermost layer of the skin is composed of dead cells which are continuously being shed as the living cells are being renewed. It is to this layer of dead cells that a sunscreen is applied. Sunscreens will variably penetrate this dead layer of skin and reach living cells depending upon their formulation.

Sunscreens are considered therapeutics rather than cosmetics and thus fall under strict regulatory requirements regarding their safety. Nevertheless some people may react adversely, with irritation or allergy. It is therefore a good idea, especially when trying a sunscreen that you have not used before, to apply a little to a small area of skin and leaving it there for as long as you can. While this may not be a sufficient self test to completely assure of an unproblematic useage, it will at least reveal whether there is any immediate irritancy. It should be remembered that with regard to anything whatsoever applied to the skin, someone, sometime, is likely to react badly to it. Recorded figures on adverse responses to sunscreens show only a very small number of people react badly and these figures have been decreasing since problematic ingredients have been identified and removed from formulations.

When

The variations of sunscreen formulations are as numerous as the number of brands available. But they share at least two characteristics; first they must contain ingredients which absorb, reflect or scatter ultraviolet energy (UV); and second, these UV-Filters, or "Actives" are dispersed within one of the two (water or oil) phases of an emulsion system.

The ideal sunscreen works by leaving a uniform film of evenly dispersed Active on the surface of the skin (or close to it). For this to happen most sunscreens require that the emulsion break during the process of applying the sunscreen to the rough surface (at the microscopic level) of the skin and then resettling.

It is this breaking and reforming of dispersed actives which require that for optimal performance a sunscreen should be applied at least fifteen (15) minutes prior to sun exposure. If you forget, or are unable to do this then the sunscreen will still work, only not as well.

Sunscreens are not like batteries. They do not run out. While a uniform film of sunscreen is maintained on the skin surface it will be doing its job of filtering a proportion of the UV energy. Some UV is getting through. With an SPF 30 your skin will have received one thirtieth (1/30th) of a sun burning dose in the same time that you would receive one (1) sunburning dose without the sunscreen. Once you have received one sunburning dose, which may not fully manifest itself for some hours, no amount of further application of sunscreen will prevent this sunburning effect. To maintain the layer of sunscreen on the skin it should be reapplied whenever it may have been rubbed off. Sweat will remove sunscreen more effectively than water. If the sunscreen is left untouched on the skin and you have to be exposed for more than two (2) hours, then it is a good idea to reapply. This will replenish whatever may have been absorbed into the skin. (If the sunscreen you are using is only SPF 8-12 or less, and you have fair skin, then it is very probable that under summer sunlight conditions at noon, you will already have accumulated a sunburning dose.

Remember

Sunscreens should be used to reduce sun exposure, and not prolong it. The meaning of the SPF value is, that with a sunscreen labelled SPF30+ (for example) properly applied, it will take at least 30 times as long to accumulate the same amount of skin damage as it would without this sunscreen. Together, with clothing, a hat, and shade, sunscreens provide a complementary means for protecting your skin from the short and long term consequences of over exposure to sunlight. These include, sunburn, premature ageing, and skin cancer.