A nipple clamp is a type of sex toy that is applied to a person's nipples to pinch them. Varieties of nipple clamp include clothes-pin-style, tweezer and clover. Nipple clamps are used to cause pain in the nipples as part of certain BDSM activities. They are also used to produce erotic stimulation as part of nipple play. In this context they are not primarily used to produce pain but rather to increase nipple sensation. Their use traps blood in the nipples, increasing the sensitivity of the nipple. The sexologist Carol Queen says that "clamps are also very useful for hands-free nipple play". The first literary depiction of the nipple clamp was in 1790, in the novel Justine by the Marquis de Sade. Forceps are also sometimes used as nipple clamps to facilitate nipple piercing. Technique As the nipples are an erogenous zone, nipple clamps can be used to heighten sensation and may lead to orgasm. BDSM practices, such as the use of a safeword, are often employed when nipple clamps are used. Before the clamps are applied the nipples are typically stimulated manually or orally to prepare them. Pulling on the nipples to elongate them makes it easier to attach the clamps. Once the nipples are erect they are held taut and the "jaws" of the clamps are closed slowly, usually on the base of the nipples where they meet the areolae as this area is less sensitive than the tip. The technique for ensuring a firm grip on the nipples varies depending on their size. Small nipples are often clamped along with part of the areolae, while large nipples are sometimes clamped without first being erected. Subsequently the tension is increased, and this is often accompanied by additional manual or oral stimulation. For safety reasons the length of time for which nipple clamps are worn is limited. Bruising and soreness can result if they are used for more than 10 minutes at a time. If the blood circulation to the nipple is cut for too long there is also a risk of damage to the tissue and nerves. Changes in skin colour can be used to determine the level of blood flow, which needs to be re-established regularly to prevent any permanent damage. When the clamps are removed the restricted blood flow rushes back into the nipples and releases oxytocin, a hormone associated with orgasm. This can make skin