Final answer:
The two most common causes of sore nipples are hormonal changes, particularly during the menstrual cycle or pregnancy, and physical irritation from factors like improper fitting clothing or intense activities.
Step-by-step explanation:
The two most common causes of sore nipples are related to hormonal changes and physical irritation. During the menstrual cycle, hormonal fluctuations involving estrogen and progesterone can cause swelling and tenderness in breast tissue, leading to discomfort in the nipples, especially during the secretory phase. This is a typical response of the breast tissue to changes in hormone levels. Another common cause of nipple soreness is physical irritation, which can result from friction due to improper fitting bras or clothing, as well as from activities such as running or other sports.
Pregnancy also results in increased hormone levels, specifically estrogen and progesterone, which lead to the development and enlargement of the mammary tissue, causing sore nipples as a side effect of this growth. Additionally, individuals who use hormonal birth control may experience similar symptoms due to the synthetic hormones that mimic the natural menstrual cycle fluctuations, affecting breast tissue in a comparable manner.