Infant formula is an artificial substitute for human breast milk. Formulas are designed for infant consumption, and usually are mostly either cow milk or soy milk. Use of infant formula has been decreasing in industrial countries for over forty years as a result of antenatal education, increased understanding of the risks of infant formula, and social activism. A 2001 report of the World Health Organization strongly advocates breastfeeding over the use of infant formula except in certain unusual circumstances.Infant formula is necessarily an imperfect approximation since:The exact chemical properties of breast milk are still unknown.A mother's breast milk changes in response to the feeding habits of her baby and over time, thus adjusting to the infant's individual growth and development.Breast milk includes a mother's white blood cells that help the baby avoid or fight off infections and give his immature immune system the benefit of his mother's immune system that has many years of experience with the germs common in their environment.