The best way to darken one's skin color is by letting the skin get tanned. Tanning is a natural process by which skin becomes dark in response to exposure to sunlight. What gives your skin its color is the pigment melanin, which is produced by certain cells in the skin that are known as melanocytes. The amount of melanin in the skin, and thus your skin color, is determined genetically, but is also influenced by your exposure to sunlight. As a protective mechanism, when your skin is exposed to sunlight it gets tanned - the melanocytes produce more melanin to block the rays of the sun, and more melanin in the skin means that the skin becomes proportionately darker. This is a natural process and is the best way to darken your skin; however, you should be warned that this is not entirely safe.
As mentioned before, tanning is a protective process - this is because sunlight contains harmful ultraviolet rays that can cause skin cancer and other skin problems. Melanin does protect the skin, but it does not provide adequate protection, especially when skin is exposed to sunlight for long periods of time. Exposure to sunlight is more dangerous if your skin has very little melanin to begin with, in which case it has less protection from UV rays.
It is best to avoid purposely exposing yourself to sunlight in order to darken your skin, but if you are going to get a tan anyway, you should take some precautions. If your skin is very light, you should try to develop a tan very gradually, to avoid excessive exposure before your skin is able to handle it. Short periods of exposure are advisable, so that your skin creates more melanin, and can then handle more sunlight. In addition, whenever possible, you should cover your skin adequately and use an appropriate sunscreen to protect it from the sun.
answered by M W