It is important to distinguish clinical lactose intolerance from hypolactasia, a low level of lactase which commonly results in malabsorption or maldigestion. Main causes of loss of lactase is the inherited loss after weaning, secondary intestinal damage due to infections such rotavirus and Giardia, or hormonal imbalance.(Usai-Satta et al., 2012) However, individuals with lactose malabsorption mostly do not develop gastrointestinal symptoms after they ingest milk products. Only people who have digestive symptoms like abdominal pain, flatulence, bloating or diarrhea are regarded and described as lactose intolerant.(Vernia et al., 2004) Lactose can also results in a range of systemic symptoms including headaches, loss of concentration, and severe tiredness.
It is also important to realize that lactose intolerance is different from a milk allergy. Allergy is an immune system respnse to foods, inducing symptoms like wheezing, itching, rashes and more and it may look similar to lactose intolarance. However, in the case of allergy, even the smallest amount of milk result in a reaction resembling to lactose intolerance. Whereas in the case of intolerance, mostly small amounts are likely be consumed without having significant problems.(Walsh et al., 2016)