Ductal ectasia or periductal mastitis: This condition is characterized by inflammation of the ducts under the nipple, leading to pain, nipple retraction, and sometimes discharge. It's a common cause of nipple pain in men and can be related to smoking or other factors.

Nipple dermatitis or eczema: Skin conditions like eczema or dermatitis can cause nipple pain and are relatively common. They can be due to allergic reactions, irritants, or atopic conditions.
Trauma or friction: Direct injury to the nipple or repetitive friction (e.g., from clothing or exercise) can cause pain and discomfort.
Gynecomastia: Although gynecomastia (breast tissue growth in men) often presents with painless enlargement, it can sometimes cause nipple pain, especially if the growth is rapid or uneven.

Breast cancer: Although rare in men, breast cancer can present with nipple pain, retraction, or discharge. It's crucial to investigate any persistent or severe nipple symptoms.
Infections (e.g., abscess or cellulitis): Infections of the breast tissue can cause severe pain, redness, and swelling. Prompt diagnosis and treatment are essential to prevent complications.
Paget's disease of the breast: A rare form of breast cancer that affects the nipple and areola, causing eczema-like changes and pain.

Sarcoidosis: A systemic disease that can cause granulomatous inflammation in various parts of the body, including the breast, leading to nipple pain.
Neurological conditions (e.g., neuropathic pain): Certain neurological conditions can cause referred pain to the nipple area, although this is less common.
Endocrine disorders: Some endocrine conditions, like hyperprolactinemia, can lead to breast symptoms, including nipple pain, although this is rare in men.