Why does hair gray?
A. There are two types of pigment or melanin that cause color in hair: eumelanin (dark brown or black) and pheomelanin (reddish yellow). Genes generally control this amount of melanin, and gray hair simply has less of it. On average, 50 percent of Caucasians, for example, are gray by age 50. It is not known how each hair loses pigment. The melanocytes, cells which produce the melanin, may be present but not active or may decrease in number. Q. What causes a hiccup? A. Hiccups are uncontrolled contractions of the diaphragm. The complete answer about their cause is not known. Common triggers for hiccups that last less than 48 hours include overeating, drinking carbonated beverages or imbibing too much alcohol. Sudden temperature changes and emotional stress also may play a role. Hiccups lasting more than 48 hours usually are due to nerve damage or irritation of the vagus or phrenic nerves; to problems affecting the central nervous system, such as stroke, tumors, and multiple sclerosis; o
