Human sexual response cycle

The human sexual response cycle is a four-stage model of physiological responses to sexual stimulation, which, in order of their occurrence, are the excitement phase, plateau phase, orgasmic phase, and resolution phase. The cycle was first proposed by William H. Masters and Virginia E. Johnson in their 1966 book Human Sexual Response. Since then, other human sexual response models have been formulated.

The excitement phase (also known as the arousal phase or initial excitement phase) is the first stage of the human sexual response cycle. It occurs as the result of physical or mental erotic stimuli, such as kissing, petting, or viewing erotic images, that leads to sexual arousal. During the excitement stage, the body prepares for sexual intercourse, initially leading to the plateau phase. There is wide socio-cultural variation regarding preferences for the length of foreplay and the stimulation methods used. Physical and emotional interaction and stimulation of the erogenous zones during foreplay usually establishes at least some initial arousal.

Among both sexes, the excitement phase results in an increase in heart rate, breathing rate, and a rise in blood pressure. A survey in 2006 has found that sexual arousal in about 82% of young females and 52% of young males arises or is enhanced by direct stimulation of nipples, with only 7–8% reporting that it decreased their arousal.Vasocongestion of the skin, commonly referred to as the sex flush, will occur in approximately 50-75% of females and 25% of males. The sex flush tends to occur more often under warmer conditions and may not appear at all under cooler temperatures.

During the female sex flush, pinkish spots develop under the breasts, then spread to the breasts, torso, face, hands, soles of the feet, and possibly over the entire body. Vasocongestion is also responsible for the darkening of the clitoris and the walls of the vagina during sexual arousal. During the male sex flush, the coloration of the skin develops less consistently than in the female, but typically starts with the epigastrium (upper abdomen), spreads across the chest, then continues to the neck, face, forehead, back, and sometimes, shoulders and forearms. The sex flush typically disappears soon after orgasm occurs, but this may take up to two hours or so and, sometimes, intense sweating will occur simultaneously. The flush usually diminishes in reverse of the order in which it appeared.

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