Why are some people lactose intolerant?

Say cheese! But if you’re lactose intolerant maybe don’t eat it? Cuz any kind of milk based food will probably give you a tummy-ache! But why? We asked pediatrician Dr. Anjuli Gans why some people are lactose intolerant… and she helped us understand what it is and why it happens. Got an udderly awesome question? Send it to us at BrainsOn.org/contact, and we’ll milk it for some answers!