This dermatologic clinical photograph depicts classic axillary acanthosis nigricans: a velvety, hyperpigmented plaque within the skin folds of the axilla. The region shows diffuse brown-to-dark pigmented, lamellar texturing with parallel linear creases and fine wrinkling along skin folds. The texture appears velvety to the touch; there is mild skin thickening and uniform pigmentation without vesicles or erosions. The lesion is localized to the axillary area, typically associated with friction and perspiration, and commonly coexists with obesity, insulin resistance, or metabolic syndrome. On histology, epidermal hyperplasia with mild hyperkeratosis and papillomatosis would be expected, though not shown here. Clinically this finding signals possible systemic associations; in adults, screen for diabetes mellitus, impaired glucose tolerance, dyslipidemia, and obesity; in older patients or atypical presentations, consider paraneoplastic acanthosis nigricans associated with gastric or other malignancies. Differential diagnoses include frictional dermatitis, candidal intertrigo, and other pigmented dermatoses. The image supports educational usage in dermatology training, primary care screening, endocrinology workups, and radiology-dermatology correlation for cutaneous signs of systemic disease. The observation underscores the importance of comprehensive clinical assessment, lifestyle modification, and targeted laboratory evaluation to identify underlying etiologies and initiate appropriate management. Careful documentation of lesion characteristics improves reproducibility and supports longitudinal monitoring over time.

This clinical photograph displays the right axilla of a patient, demonstrating classic features of acanthosis nigricans. The primary finding is a large, focal area of brownish hyperpigmentation with a velvety or 'dirty' appearance. The skin texture within the affected region is notably altered, exhibiting lichenification and verrucous-like thickening with a non-uniform surface. Along the periphery and within the hyperpigmented plaque, several small, pale, pedunculated lesions resembling acrochordons (skin tags) are visible. The surrounding skin appears normal in color and texture. This presentation is characteristic of paraneoplastic acanthosis nigricans, often associated with underlying malignancies or metabolic conditions such as insulin resistance and type 2 diabetes. The educational focus of this image is the recognition of cutaneous markers for systemic disease and the distinctive morphological features of epidermal hyperproliferation in intertriginous areas.

This clinical photograph displays a close-up view of the right axillary region of a patient, demonstrating classic features of acanthosis nigricans. The central axilla shows a poorly demarcated, symmetrical area of hyperpigmentation, characterized by a brownish to grayish-black discoloration that is markedly darker than the surrounding skin. The skin texture within the affected zone appears thickened with a velvety, rugose, or 'dirty' appearance, particularly visible along the natural skin folds. Terminal axillary hair is present, predominantly concentrated over the lower half of the hyperpigmented plaque. The image captures the transition between the medial upper arm and the lateral thoracic wall, providing anatomical context. In a clinical setting, this finding is often associated with insulin resistance, obesity, or certain medications, such as isoniazid as noted in this case, and serves as an important dermatological marker for underlying metabolic or systemic conditions.