There is a small hard lump under the armpit that hurts when pressed.

Under normal circumstances, the appearance of a small hard lump in the armpit accompanied by pain upon pressure may be caused by various factors such as the female menstrual cycle, exercise or trauma, folliculitis, lymphadenitis, or sebaceous cysts. It is recommended to seek medical attention promptly, identify the underlying cause, and receive symptomatic treatment under the guidance of a qualified physician. Specific analyses are as follows:

1. Female Menstrual Cycle

During the menstrual cycle, hormonal fluctuations may lead to breast tissue proliferation, which can sometimes affect the lymph nodes in the armpit area, causing slight swelling and mild pain. Avoid wearing tight clothing to reduce pressure on the armpit.

2. Exercise or Trauma

Intense physical activity or accidental impact may cause injury to muscles, ligaments, or skin in the armpit area, resulting in a localized inflammatory response that presents as a hard lump with pain. Treatment includes rest, ice application, and topical or oral analgesics such as ibuprofen tablets or ketoprofen gel patches.

3. Folliculitis

Folliculitis is usually caused by bacterial infection. In the armpit, where sweat and bacteria tend to accumulate, folliculitis can easily develop, forming painful lumps accompanied by redness, swelling, and tenderness. Under professional medical guidance, medications such as mupirocin ointment, erythromycin ointment, or doxycycline hydrochloride tablets may be used to relieve symptoms.

4. Lymphadenitis

Lymphadenitis is typically caused by bacterial infection. In the armpit, it may present as a localized hard lump with pain, possibly accompanied by systemic symptoms such as fever and fatigue. Medications such as amoxicillin capsules, levofloxacin hydrochloride tablets, or ciprofloxacin hydrochloride tablets may be taken as directed by a physician.

5. Sebaceous Cyst

A sebaceous cyst occurs due to blockage of the sebaceous gland duct. When sebum production is high and ducts are prone to obstruction, cysts can form, appearing as firm lumps protruding from the skin surface. These may be painful upon pressure and could become red, swollen, or even purulent. Treatment under medical supervision may include tetracycline ointment, cefaclor capsules, or roxithromycin dispersible tablets.

In daily life, maintain healthy habits, eat a balanced diet, and engage in appropriate physical activity.