What symptom is most commonly associated with mastitis?

Mastitis is an inflammation of the breast tissue that can result from infection, often occurring in women who are breastfeeding, although it can occur in non-lactating women as well. The hallmark symptoms of mastitis include breast swelling and tenderness, which arise due to inflammation and possibly infection. The swelling occurs because of the accumulation of fluid and inflammatory cells in the breast tissue, while tenderness can develop as a direct result of inflammation and sensitivity in the affected area.

In contrast, sudden weight loss, increased appetite, and regular menstrual pain are not characteristic of mastitis. Sudden weight loss can indicate various systemic issues, while increased appetite can relate to other conditions or metabolic changes. Regular menstrual pain typically pertains to cyclic hormonal changes and does not directly relate to the localized breast issues seen in mastitis. Thus, breast swelling and tenderness distinctly identify mastitis as a condition, making it the correct symptom associated with this condition.