The sunlight has three broad spectrums:

1. Visible light  has a wavelength between 400 and 760 nm.

2. Ultraviolet rays (less than 400 nm) are divided into three groups:

  (i) UVA (320-400 nm), 
 (ii) UVB (280-320 nm), and
(iii) UVC (200-280)

The UVC rays are mostly absorbed by the ozone layer of the outer atmosphere.

The UVB rays are harmful for the skin, particularly during the midday period (4 to 6 hours), when they are in maximum amounts in the sunlight.

The UVA rays are responsible for ageing of the skin.

The Infrared radiations are above 760 nm.

Sun Protection Factor (SPF)

The sunscreen lotions are graded according to the SPF as SPF15 SPF 30, SPF 40, or SPF 50.

UVB protection is adequately offered by SPF 15 and SPF 30.

strength lotion(s).

SPF 50 lotion prevents damage due to both UVA and UVB rays.

Sunscreens

The chemical nature of sunscreens protects the skin from the harmful effects of sun rays. Research has evolved and developed agents which prevent sunburns, and may be used for the prevention of skin cancer. It is known that lighter skin is more easily damaged than darker skin. These chemical agents block, scatter, or absorb UV rays and protect the skin. Some of the chemicals are listed below:

1. Paraaminobenzoic acid (PABA): This UV filter absorbs UVB, the radiation that causes sunburn.

2. Benzophenones: These organic chemical compounds absorb UVA, which is linked to melanoma, a deadly skin cancer.

3. Anthranilates: These chemicals absorb both UVA and UVB.

There are several other organic and inorganic chemicals that block or scatter the rays, and prevent radiation damage to the skin.

Precautions and mode of use

(a) Sunscreens are most effective if applied 30 minutes before exposure to the sun.

(b) Sweating or swimming can wash away the sunscreen.

(c) Its application should ideally be repeated ever 2 hours.

(d) Sunscreen application indiscriminately can lead to vitamin D deficiency. Exposure to sun provides vital doses of vitamin D needed for the development of strong bones. Its deficiency can lead to rickets in children, and osteomalasia in adults.

(e) Sunscreen must be applied to all areas of the skin exposed to the sun, and should be rubbed into the skin completely. If still sunburn cannot be avoided then stay away from bright sunlight, or try a preparation with a higher SPF value.

(f) Don"t forget to reapply the sunscreen after profuse sweating or swimming.

These are some of the precautions to be taken if one is vulnerable to sunburns.