[Fmeub]

Hi!

There is a rumour/story/myth that if you put lemon juice on your hair and sit in the sun, it will bleach your hair. It has also been observed, that at the beach my hair bleaches faster than further inland where I live. That is, my hair colour becomes lighter and more blonde.

So firstly, I have been wondering what in the lemon juice would cause the bleach, -if at all.
Secondly, at the beach, I guess it is the salt (anions?) in the seawater that cause the bleaching effect?
Thirdly, if I dissolve NaCl in lemon juice, would it enhance the bleaching effect?
Fourthly, the sunlight gives the energy (hv), but what does it promote to a higher energy level, or does it just act as a catalyst for whatever takes part in the reaction?

 

Thanks!

[bromidewind]

Oxidation, oxidation, oxidation.

Lemon juice is comprised mostly of citric acid, which happens to be a weak oxidizer. The same reason why sodium hypochlorite (bleach) bleaches your hair is the same reason why lemon juice bleaches your hair. Adding NaCl to lemon juice won't really do anything. If you really want to bleach your hair, just go buy some bleach or hair dye. The salt in the water isn't really adding to the bleaching effect. Go to a freshwater lake, and you'll probably see similar results. The reason that it "seems" to bleach faster when you're by salt water is that when you go to the beach, you stay outside the whole time for several hours. When you're inland, you're constantly passing through shade and going indoors and outdoors.

As for the sunlight, I found this on TheNakedScientists website

the reason is that hair is a filament of protein that's produced by a hair follicle and extruded out through the skin. Within the hair follicle populations of cells called melanocytes add forms of melanin called phaeomelanin and eumelanin to the hair, giving it its colour.

But once the hair leaves the follicle and grows out onto your scalp it is beyond the reach of the melanocytes and therefore the melanin it carries cannot be replaced; sunlight falling on the hair can therefore photolyse (break apart) the melanin molecules, bleaching the hair.

Skin is different. A suntan is the result of damage to the basal layers of the skin by ultraviolet rays. This UV stimulus triggers melanocytes to increase their activity, adding more melanin to the overlying skin. As the cells are present, more sun means more UV and this means more melanocyte activity meaning more melanin. Unlike the hair the permanent presence of the melanocytes means they can alter the composition of the overlying skin.

http://www.thenakedscientists.com/forum/index.php?topic=17341.msg197564#msg197564