Hidden pain under the right armpit may be related to localized folliculitis in the armpit and female breast enlargement. Localized skin infections in the armpit can cause the dermal capillaries to dilate and fill with blood, which can lead to redness and tenderness. The pain is usually mild and insidious, and is more pronounced in deeper locations. It is often accompanied by localized skin rashes and pustules in the armpits. Mammary hyperplasia is a common breast disease in women, the typical symptoms are cyclic breast pain, breast lumps and nipple discharge, which can lead to axillary lymph node pain, resulting in symptoms of axillary tenderness. Lymph node pain in the lower part of the armpit may be caused by lymphadenitis, trauma to the chest wall, or rib lesions. Therefore, it is important to consult a doctor for a clear diagnosis and follow the doctor’s instructions.