Sunscreens

  

    Sunscreen (also commonly known as sun screen, sunblock, suntan lotion, sunburn cream, sun cream or block out) is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation on the skin exposed to sunlight and thus helps protect against sunburn. Skin-lightening products have sunscreen to protect lightened skin because light skin is more susceptible to sun damage than darker skin. A number of sunscreens have tanning powder to help the skin to darken or tan; however, tanning powder does not provide protection from UV rays. Depending on the mode of action, sunscreens can be classified into physical sunscreens (i.e., those that reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light).

  

  The use of sunscreens in recent years has increased due to heightened concern over the risk of skin cancer and other conditions caused b

y exposure to UV radiation. in DNA, for example, UV radiation can cause adjacent thymine bases to form mutagenic dimers. Sunscreens afford protection from radiation because they contain aromatic molecules that absorb energy in the UV region of the electromagnetic spectrum. Absorption of UV radiation by these molecules promotes π and nonbonding electrons to higher energy levels, after which the energy is dissipated by relaxation through molecular vibration. In essence, the UV radiation is converted to heat (IR radiation).

  

  Sunscreens are classified according to the portion of the UV spectrum where their maximum absorption occurs. Three regions of the UV spectrum are typically discussed. The region from 320 to 400 nm is called UV-A, the region from 280 to 320 nm is called UV-B, and the region from 100 to 280 nm is called UV-C. the UV-C region is potentially the most dangerous because it encompasses the shortest UV wavelengths and is therefore of the highest energy. However, ozone and other components in Earth’s atmosphere absorb UV-C wavelengths, and thus we are protected from radiation in this part of the spectrum so long as earth’s atmosphere is not compromised further by ozone-B radiation passes through the atmosphere to reach us, and it is against these regions of the spectrum that sunscreens are formulated. Tanning and sunburn are caused by UV-B radiation. Risk of skin cancer is primarily associated with UV-A radiation, although some UV-A wavelengths may be important as well.

   The specific range of protection provided by a sunscreen depends on the structure of its UV-absorbing groups. Most sunscreens have structures derived from the following parent compounds: p-aminoibenzoic acid (PABA), cinnamic acid (3-phenylpropenoic acid), benzophenone (diphenyl ketone), and salicylic acid (o-hydroxybenzoic acid). The structures and λmax for a few of the most common sunscreen agents are given below. The common theme among them is an aromatic core in conjugation with other functional groups.

octyl 4-N,N-dimethylaminobenzoate

2-Ethylhexyl 4-methoxycinnamate

2-Hydroxy-4-methoxybenzophenone