But sunlight isn’t the whole story. The study also points to the role of repeated friction. Watches, bracelets, tight clothing—constant rubbing can sometimes trigger localized hyperpigmentation. The body reacts to the irritation by toughening the area, and in some cases, by darkening the skin.

Hormones are another factor highlighted by researchers. Certain stages of life, such as pregnancy or menopause, bring visible changes. Hormonal shifts directly affect pigment production, which explains why spots can appear even without sun exposure.

The Impact of Diet and Stress

The study didn’t stop at physical factors. It also looked at the connection between nutrition and skin health. What you eat matters. Vitamin deficiencies—especially vitamin B12—can throw off the skin’s balance, leaving some areas dry while others darken.

Chronic stress also plays a role. Under constant pressure, the body releases cortisol. Too much of this hormone disrupts normal cell function. The skin becomes uneven, and irregular or diffuse spots may appear.

Certain cosmetic products can make things worse. Perfume on the neck, harsh deodorants, or unsuitable creams can all irritate the skin and trigger pigmentation. The study recommends always testing a new product on a small patch before regular use.

Finally, genetics weigh in. If your parents developed spots on their arms or face, your chances are higher too. But nothing is set in stone. Simple habits can help reduce their appearance.