Acanthosis Nigricans: This condition is characterized by hyperpigmented, velvety plaques in flexural areas such as the axillae, groin, and between the thighs. It is often associated with insulin resistance and obesity, which are common in the female population.

Erythrasma: A bacterial infection caused by Corynebacterium minutissimum, which thrives in warm, moist areas of the body. It presents as hyperpigmented macular lesions, typically in the groin and between the thighs.
Tinea Cruris (Jock Itch): A fungal infection that affects the groin area and can spread to the thighs. It may present with hyperpigmented lesions, especially in darker-skinned individuals.
Seborrheic Dermatitis: An inflammatory skin condition that can cause hyperpigmented macular lesions in flexural areas, including the axillae and groin.

Addison's Disease: A rare endocrine disorder characterized by adrenal insufficiency, which can cause hyperpigmentation of the skin, including the axillae and groin. Although rare, it is crucial to consider due to its potential severity.
Malignancy (e.g., Lymphoma): Certain types of lymphoma, such as mycosis fungoides, can present with hyperpigmented skin lesions. Early detection is critical for effective treatment.

Nevus of Ota: A congenital condition characterized by hyperpigmentation along the ophthalmic and maxillary branches of the trigeminal nerve, but it can also appear in other areas, including the axillae and groin.
Erythema Dyschromicum Perstans: A rare condition of unknown etiology, characterized by hyperpigmented macular lesions that can appear anywhere on the body, including the axillae and groin.