This is chemically dyed.

According to the conclusion drawn by the Consumers Association, some dye compounds will release carcinogens, just like efficient plasters attached to the skin, which will cause human diseases through the action of sweat and body temperature. Medical experiments show that toxic substances act on clothes even faster than through diet. A urologist in Japan claims that the increase of cystitis among Japanese women is mainly due to wearing chemical fiber underwear. Not only that, fashion style may also do harm to human body. Wearing tights as usual will do harm to the body to varying degrees.