katyzzzWorking of Sunburn and Sun Tans
August 5th 2006 04:40
Working of Sunburn and Sun Tans :
There is something mysterious about the sun and skin. Why is it that if you go out on a bright summer day and spend an hour in the sun, you get a sunburn? You get a sunburn, that is, unless you happen to have taken the time to get a nice gradual tan. With a nice tan you can go out in the sun and nothing happens. Of course, that doesn't apply if you have "fair skin." The fair skinned among us never get a tan, so they always get sunburned. Unless of course they are wearing a sunscreen...
Does this make sense? What the heck is a sunscreen? And what is a tan? What is the difference between a tan and a burn? Why can you spread a little blob of lotion on yourself and be protected, but if you forget you are miserable?
Skin and working :
Skin is one of the most amazing organs in the human body. It is hard for us to think about it as an organ, however. We tend to think of organs as boxy things. Your heart, liver, kidneys - those are obviously organs. But skin is an organ too, especially if you look at the dictionary definition of "organ", like this definition from the Merriam Webster Collegiate Dictionary:
Organ - a) differentiated structure (as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism b) bodily parts performing a function or cooperating in an activity <the eyes and related structures that make up the visual organs>
Tanning, Sunburn and Sunscreen :
When you get a tan, what is actually happening is that the melanocytes are producing melanin pigment in reaction to ultraviolet light in sunlight. Ultraviolet light stimulates melanin production. The pigment has the effect of absorbing the UV radiation in sunlight, so it protects the cells from UV damage. Melanin production takes a fair amount of time - that is why most people cannot get a tan in one day. You have to expose yourself to UV for a short period of time to activate the melanocytes. They produce melanin over the course of hours. By repeating this process over 5 to 7 days pigment builds up in your cells to a level that is protective.
The previous paragraph applies to Caucasians. In a variety of other races melanin production is continuous, so the skin is always pigmented to some degree. In these races the incidence of skin cancer is much lower because cells are constantly protected from UV radiation by melanin.
Sunburn :
Sunburn is a popular term applied to the marked erythema and pain that commonly follows injudicious sun exposure. A sunburn is really a delayed ultraviolet B-induced erythema caused by an increase in blood flow to the affected skin that begins about 4 hours and peaks between 8-24 hours following exposure. The underlying cause of this vascular reaction is direct and indirect damage to specific cellular targets from photochemical reactions and the generation of reactive oxygen species.
Sunscreens :
Sunscreens block or absorb ultraviolet light. You can block UV with opaque creams like the white zinc oxide cream that you see lifeguards putting on their noses. You can also absorb UV radiation in much the same way that melanin does. The first and most common of the absorption chemicals is PABA (para-aminobenzoic acid). It absorbs UVB. If you have sensitive skin, take care when using sunscreen with PABA as it may cause irritation or an allergic reaction in some individuals. Other sunscreen chemicals include:
Cinnamates absorb UVB.
Benzophenones absorb UVA.
Anthranilates absorb UVA and UVB.
Ecamsules absorb UVA.
There is something mysterious about the sun and skin. Why is it that if you go out on a bright summer day and spend an hour in the sun, you get a sunburn? You get a sunburn, that is, unless you happen to have taken the time to get a nice gradual tan. With a nice tan you can go out in the sun and nothing happens. Of course, that doesn't apply if you have "fair skin." The fair skinned among us never get a tan, so they always get sunburned. Unless of course they are wearing a sunscreen...
Sun Tans and Sunburn
Skin and working :
Skin is one of the most amazing organs in the human body. It is hard for us to think about it as an organ, however. We tend to think of organs as boxy things. Your heart, liver, kidneys - those are obviously organs. But skin is an organ too, especially if you look at the dictionary definition of "organ", like this definition from the Merriam Webster Collegiate Dictionary:
Organ - a) differentiated structure (as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism b) bodily parts performing a function or cooperating in an activity <the eyes and related structures that make up the visual organs>
Tanning, Sunburn and Sunscreen :
When you get a tan, what is actually happening is that the melanocytes are producing melanin pigment in reaction to ultraviolet light in sunlight. Ultraviolet light stimulates melanin production. The pigment has the effect of absorbing the UV radiation in sunlight, so it protects the cells from UV damage. Melanin production takes a fair amount of time - that is why most people cannot get a tan in one day. You have to expose yourself to UV for a short period of time to activate the melanocytes. They produce melanin over the course of hours. By repeating this process over 5 to 7 days pigment builds up in your cells to a level that is protective.
The previous paragraph applies to Caucasians. In a variety of other races melanin production is continuous, so the skin is always pigmented to some degree. In these races the incidence of skin cancer is much lower because cells are constantly protected from UV radiation by melanin.
Sunburn :
Sunburn is a popular term applied to the marked erythema and pain that commonly follows injudicious sun exposure. A sunburn is really a delayed ultraviolet B-induced erythema caused by an increase in blood flow to the affected skin that begins about 4 hours and peaks between 8-24 hours following exposure. The underlying cause of this vascular reaction is direct and indirect damage to specific cellular targets from photochemical reactions and the generation of reactive oxygen species.
Sunscreens :
Sunscreens block or absorb ultraviolet light. You can block UV with opaque creams like the white zinc oxide cream that you see lifeguards putting on their noses. You can also absorb UV radiation in much the same way that melanin does. The first and most common of the absorption chemicals is PABA (para-aminobenzoic acid). It absorbs UVB. If you have sensitive skin, take care when using sunscreen with PABA as it may cause irritation or an allergic reaction in some individuals. Other sunscreen chemicals include:
Cinnamates absorb UVB.
Benzophenones absorb UVA.
Anthranilates absorb UVA and UVB.
Ecamsules absorb UVA.
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