The Similac Lactose Free Formula is sensitive to baby's fussiness and gas. Most babies do just fine on a milk based formula containing lactose, such as other Similac formula, but some babies may be sensitive to the lactose or milk sugar in the baby formula. Sensitivity simply means a reaction such as diarrhea, gas, fussiness or other feeding problems. Lactose Free Formula from Similac is a milk based baby formula, but contains no lactose. It is the perfect Similac formula for parents concerned with their baby's sensitivity to lactose, but still prefer a milk-based formula. Before selecting a baby formula from Similac consult a pediatrician.