Physical changes due to puberty start occurring by the age of 14 years. Earliest change is the growth of testes, then the growth of penis. Genital development occurs from 11-15 years. Sperm production, which begins in childhood, becomes fully established during puberty. Ejaculation starts, which results in nocturnal emissions and Masturbation. Pubic hair growth begins around this time followed a year or two later by the facial and axillary hair. There is growth of body hair. Deepening of the voice is another major change in puberty and is more evident in boys. Rising hormone levels, during puberty contribute to an activation of sexual sensations and erotic thoughts and dreams.