Sunscreens are the agents which protect the skin from sunlight. Two types of agents: (1) reflectors, and (2) absorbers, can act as sunscreens. Reflectors are substances which when present on the skin surface reflect the rays of light in other directions and thus, prevent them from entering the skin.
These are active against all wavelengths of sunlight. Absorbers, on the other hand, absorb the sunlight and therefore, these are active against only a specific spectrum of sunlight. The following agents can be used alone or in combination with each other to act as sunscreens, but it is important to remember that sunscreens need to be applied only as long as there is daylight, it is no use applying sunscreens at night.
Moreover, the effect of a topical sunscreen does not last for more than a few hours. The author therefore, as a rule, recommends three applications during the day the first one after the bath in the morning, the second at about 12 noon and the third at 4 p.m. or so. An additional application will be useful just before going outdoors during the day.
Para-aminobenzoic: This is a white powder which has been extensively used as a sunscreen in the form of five to ten percent ointments or creams. A five to ten percent concentration in 70 to 95 percent alcohol with or without 40 percent glycerine has been found to be one of the most effective sunscreens. It absorbs light in the ultraviolet (UVB) range and thus, it is very useful for dermatoses caused by the sunburn spectrum of light.
Benzophenones: Two compounds, hydroxyl-and dihydroxymethoxy-benzophenones absorb sunlight in the long. Ultraviolet (UVA) range with a slight overlap in the visible spectrum. These agents can be used as a ten percent concentration in a cream base.
Tannic acid: It is a light brown, water soluble powder which is mostly used as an astringent on mucous membranes. A five to ten percent concentration in a cream base can also absorb light in the ultraviolet range and act as a sunscreen.
Titanium dioxide: It is a reflector of sunlight active against a wide spectrum of radiations. A ten percent concentration alone or with other ingredients in an ointment can act as good sunscreen.
Zinc oxide and calamine: Both these agents are also reflectors of sunlight and can be mixed with other sunscreen preparation. Calamine lotion used as such also acts as sunscreen.