Contrary to popular belief, hair does not always grow faster in the summer. Faster hair growth is contributed to other factors besides the weather.
While a small percentage of people experience faster hair growth in the summer due to repeated light exposure, how fast the average person's hair grows depends more on genetic factors. Other things that affect the rate of hair growth includes a person's diet and the hormone levels in the body. A person who maintains a healthy diet rich in fruits and vegetables, and has a normal hormone balance, is more likely to see rapid hair growth.