A shirt is an item of clothing worn on the upper body. Most shirts have a collar and long sleeves, and do up at the front using buttons. However, short-sleeved shirts, collarless shirts and shirts with other fastenings are reasonably common. Most shirts are made from a light material such as cotton, or synthetic fibers such as polyester which require less ironing, or a blend of more than one type of fabric. In the sixteenth century, pious men who believed that they had sinned would sometimes wear a hair shirt as penance, as the garment was deliberately uncomfortable. The women's equivalent of a shirt is often called a blouse. The team uniforms of soccer teams are known as shirts, although they have no buttons and more resemble T-shirts. The word 'shirt' derives from the same root as 'skirt', even though in the present day they refer to two completely different types of garb. On formal occasions, men are generally expected to wear a shirt underneath a jacket.