Skin at the sites where spots develop
At the sites where spots develop, excessive melanin formation constantly takes place. Shiseido compared the skin at the site of a spot with that at a normal site histologically, and discovered that inflammatory cells are more abundant at the site of the spot than at the normal site (the inflammation at the spot site is extremely slight and does not manifest as redness, swelling or pain). It was also discovered that the number of activated melanocytes (melanin-producing cells) to total melanocytes is higher at the spot site than at the normal site. From these results, we may assume that melanocytes remain activated because of "a chronic, mild inflammatory condition" and excessive melanin formation thus persists at the site of the spot.
Melanin is also formed outside of melanocytes
Shiseido has found that the quick skin darkening under the sun is due to the colorless pre-melanin DHICA (precursor of melanin) which has accumulate in the epidermis is converted to melanin upon exposure to ultraviolet A rays (long wave length). It has also become clear that melanin, which so far has been considered to be formed only in melanocytes, is also formed outside of melanocytes.
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Irradiation of human skin with UVA equivalent to 1-2 hours of exposure to sunlight in the summer. The skin sample was collected at 3 hours after irradiation, and microscopically examined. The cells around basal layer (yellow dotted line) turned black in a short time. |
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When transparent DHICA solution was irradiated with UVA equivalent to about 20 minutes of exposure to sunlight in the summer, pre-melanin was converted to melanin in a short time. |
Whitening agents made by Shiseido (active ingredients of quasi-drugs)
m-Tranexamic acid
m-Tranexamic acid acts on the chronic mild inflammatory condition at the sites of spots, to suppress melanocyte activation. Shiseido verified the whitening effect of products containing tranexamic acid applied to the skin, and developed it as a quasi-drug active ingredient.
Arbutin
Arbutin, known to be contained in cowberries, inhibits the action of tyrosinase, an enzyme indispensable to the formation of melanin, i.e., it has the effect of preventing spots by suppressing excessive formation of melanin.
Stabilized vitamin C derivative (AA-2G)
One of the derivatives of vitamin C, which is unstable in aqueous solutions, with improved stability of vitamin C. AA-2G is converted to pure vitamin C by an enzyme present in the skin, to show a whitening effect.
Vitamin C ethyl (3-0-ethyl ascorbic acid)
A derivative of vitamin C that is the most recently developed whitening agent. Vitamin C ethyl acts rapidly, and gives the skin a translucent appearance
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