Lactose intolerance has some frequent symptoms, some of them are: abdominal pain, diarrhea, abdominal bloating, flatulence and sickness..

Symptoms usually appear from 30 minutes to 2 hours after consuming dairy products and products containing lactose (including medicines). Symptoms range from mild to severe, based on the amount of lactose consumed and the amount a person can tolerate, and disappear between 3 and 6 hours later, even though in some cases can last for days.

Symptoms occur because the unabsorbed lactose passes through the small intestine and into the colon and they are converted by intestinal bacteria producing hydrogen and other gas.

Symptoms range from mild to severe based on the amount of lactose consumed, the amount of lactase a person has and his/her bacterial flora.

There are 3 types of Hypolactasia or Lactose Intolerance:

Primary hypolactasia or primary deficiency of lactase is connected with the appearence of determined polymorphisms in the regulating region of the lactase gen. These polymorphisms seem to be associated to the persistence of lactase. Adult hypolactasia is the most common type of hypolactasia. It usually appears within few years after birth. It is developed in a progressive way. Its prevalence varies according to ethnic groups, moment or age in which enzymatic activity begins decline seems to be determined genetically depending on the ethnic group.

Secondary hypolactasia is an acquired type caused by a diffuse lesion in the intestinal mucosa affecting enzymatic activity of lactase. It appears in people with an activate enzymatic activity. A diffuse lesion of the intestinal mucosa has different causes including: diseases of the small intestines, multisystem diseases and iatrogenic causes related to a condition, disease or disorder due to medical treatments or drugs.

Congetinal hypolactasia or congenital deficiency of lactase. This is a very rare case with few documented instances in the world. It is determined by an autosomal recessive alteration of the regulating region of the lactase gen. It is characterized by a significant reduction of lactase from birth and it persists throughout the lifetime. If not diagnosed and treated quickly it has a fatal prognosis.