Marasmus is a disorder of malnutrition that is a result of total calorie starvation, especially protein and energy. It is often seen in infants under 1 year of age, most commonly in developing countries. The decreased nutrition is usually secondary to weaning problems resulting from disease, poor hygiene, poverty, and cultural factors. Infants with repeated bouts of gastroenteritis are particularly at risk.

The infants are emaciated with loss of the subcutaneous fat and muscle. The skin is dry and loose. They also have thin, fragile hair and nail abnormalities.