Some changes occurs due to the hormone secretions(in both boys and girls)-
1. Thick hairs growing in the new parts of the body such as armpit and the genital area between thigh, which can also become darker in colour.
2. Thinner hair can also appear in legs and arms, as well as on the face.
3. The skin frequently becomes oily and pimples begins to develop.
Changes in Boys-
1. New thick hair growth on their face.
2. Their voices begins to crack.
3. The penis occasionally begins to become enlarged and erect, either in daydreams or night.
Changes in Girls-
1. Breast size begins to increase, with darkening of the nipples at the tips of the breast.
2. They begin to menstruate at around this time.