2. Armpits

Dark patches in the armpits can sometimes be connected to deodorants or friction, but when the skin becomes unusually thick and almost velvety, it may be a warning sign. Can:cer-related acanthosis nigricans often shows up in hidden areas like the underarms, and may appear suddenly without clear cause.

3. Groin

The groin is another region where abnormal skin darkening may happen. Because it is usually covered, changes can go unnoticed for a long time. If the skin in this area becomes darker, itchy, or rough in texture, and the change progresses quickly, it is worth seeking medical evaluation. Some internal cancers, particularly stomach or liver cancers, have been linked to pigmentation in this area.

4. Elbows and Knees

Most people have slightly darker elbows and knees due to pressure and friction. However, a sudden and dramatic change in shade especially when mixed with a thicker texture could be a red flag. If lotions or exfoliation do not enhance  the condition, and the darkening seems to worsen, this may signal that something deeper in the body is affecting skin health.