siddha yoga

[crickets chirp] [cymbal plays] [chime plays] [narrator:] skin covers all our bodies, but its color variesfrom person to person. to understand why,we need to peer inside its layers. [music plays] skin cells and their allies--hair, sweat and oil glands--form a first lineof defense from the environment.

skin's three main layers are each a distinct community of cellswith different jobs. to see what gives skin its color, we need to focuson the outermost layer-- the epidermis-- and two important cell types:keratinocytes and melanocytes. the keratinocytes are the cellsthat form the surface of the skin and are on the frontlinefor taking insults from the environment. deeper down in the epidermis,right at the base of the layer,

we find the melanocytes. these star-shaped cellsproduce the important pigment melanin. let's zoom inside a melanocyteto see how this works. melanin is produced inside what looklike spheres throughout the melanocyte. these are the melanosomes. chemical reactions inside melanosomesturn the amino acid tyrosine into melanin. the proportion of two main formsof melanin produced-- a reddish-yellow typeversus a black-brown type;

the total amount of melaninin each melanosome; and the number of melanosomesin the epidermis-- all vary from person to personand determine their skin color. melanosomes are the melanin factoriesinside melanocytes. but for melanin to do its job, melanosomes need to be transportedto the keratinocytes via the melanocytes' long projections. inside the keratinocytes, some melanosomes form a caparound the cell nucleus.

the melanin inside the melanosomes absorbs the ultraviolet energyfrom sunlight, reducing the amountof ultraviolet radiation that reaches the nucleus and,in particular, the dna inside the nucleus. ultraviolet radiation can cause mutations in dnathat can lead to cancer. when ultraviolet radiation increases,melanin production increases, and more melanosomesare delivered to keratinocytes.

most people can adjustto greater exposure to the sun by turning upmelanin production and tanning. but their genetic inheritance determines both the baseline colorof their skin and how much it can tan.