Similac Pro-Sensitive helps strengthen your babys immune system to be more like a breastfed baby than ever before. How? Similac with 2-FL helps support babys developing immune system by closing multiple gaps in immune function* between formula-fed and breast-fed infants. Unlike other formulas, Similac has 2-FL HMO, a prebiotic that circulates throughout the body. Our sensitive formula is designed for fussiness and gas due to lactose sensitivity.