Is it not due to lack of certain vitamins in the human body system?

• Vitamin deficiencies typically cause different types of skin changes, such as:
  • Pellagra (niacin deficiency) can cause dark, rough skin in sun-exposed areas, but it has a distinct pattern and texture.
  • Vitamin B12 deficiency can sometimes cause hyperpigmentation, but it's usually more generalized or in specific areas like knuckles, not isolated, irregular patches like those seen.
  • Other deficiencies might lead to dry skin, rashes, or poor wound healing.

The dark patches in the image you sent had an irregular, smudged appearance consistent with external dirt or residue rather than a systemic skin condition caused by a nutritional deficiency.