Nipple swelling during ovulation is a common physiological phenomenon, also known as "nipple enlargement" or "nipple swelling". This phenomenon usually occurs a few days before ovulation and can be caused by a variety of factors, such as hormonal changes, infection, or allergies.

Nipple enlargement may be caused by one of the following reasons:

1. Hormone changes: During ovulation, a woman’s body hormone changes and HCG levels increase, which may cause edema of the tissue around the nipple and areola.

2. Infection: Nipple enlargement may also be caused by infection of the tissue around the nipple, such as fungal infection or bacterial infection.

3. Allergies: Certain allergic reactions may also cause nipple enlargement and swelling.

4. Others: Sometimes, nipple enlargement may also be caused by other factors, such as malnutrition, thyroid problems, etc.

Although nipple swelling during ovulation is a common physiological phenomenon, some people may experience discomfort or pain. If you feel discomfort or pain, it is recommended to seek medical advice promptly so that a diagnosis can be made and appropriate treatment can be taken.

In addition, some people may feel curious or ashamed about nipple enlargement, but this phenomenon is usually a normal physiological phenomenon and there is no need to feel uncomfortable or ashamed.