According to the International Skating Union, the governing body of figure skating, “Ladies must wear a skirt. The Ladies dress must not give the effect of excessive nudity inappropriate for an athletic sport. Men must wear full-length trousers: no tights are allowed and the man’s costume may not be sleeveless.”
The rule for female figure skaters to wear skirts was introduced after Debi Thomas dressed inappropriately (as per ISU) at the 1988 Olympics. The credit for introducing the short skirt to women’s figure skating goes to Sonja Henie of Norway who won Gold medals in 1928,1932 and 1936.