Lactase is an enzyme that is produced in the digestive system of all babies and some adults - mostly Europeans or people with European roots. This enzyme is absolutely necessary for the breakdown of milk and dairy products by the body.
The main function of the enzyme lactase is to break down lactose - a disaccharide compound of the simple monosaccharides galactose and glucose . Lactose makes up from 0.5% to 8% of the weight of fresh milk and in addition to human milk is found in all dairy products - yogurt, cheese, cheese, cottage cheese, ice cream, sour cream, ice cream and more.
Everyone is born with high levels of lactase in their body - the enzyme is vital because without it it would be impossible to process breast milk . However, with weaning in most people, levels of this enzyme gradually fall to an absolute minimum, no longer recover, and a deficiency of the molecule called hypolactasia - lactose intolerance - occurs
In a small part of the world's population, this enzyme is also present in adults and gives them lactose tolerance . This is due to a genetic mutation that occurred 8,000-10,000 years ago in human populations involved in cattle breeding and dairy farming. Today, their descendants are able to use milk and dairy products as food even after childhood, because their ability to produce the enzyme lactase in adulthood has evolved over the millennia.
Symptoms of lactose intolerance are caused by the body's inability to break down lactose-containing products. Undigested lactose becomes toxic in the digestive tract and, depending on the amount of dairy product ingested, symptoms vary: bloating and painful stomach cramps, uncontrolled flatulence, diarrhea, nausea and vomiting, fatigue and dizziness. They occur 30 to 120 minutes after ingestion of a product containing lactose.
However, some of these symptoms overlap with those of milk allergy, which creates the preconditions for misdiagnosis . Allergy is different from intolerance . While allergies are due to the body's over-strong immune response to foreign matter, intolerance develops due to the lack or deficiency of the enzyme needed to break down - the immune system does not intervene in this case. 
Milk allergy affects about 50 million people worldwide or from 0.3% to 0.5% of the population. It is important to recognize it in time, because unlike intolerance, which is rather an inconvenience for modern man, allergies can be fatal, especially in individuals aged 8 to 16 years.
Symptoms of milk allergy range from gastrointestinal to cutaneous and respiratory. Often the first attack of milk allergy begins with a mild skin rash and itching, vomiting, stomach pain, constipation, rhinitis and flatulence - can easily be mistaken for intolerance. However, without medical intervention or adequate medication, the condition can quickly escalate to allergic colitis, shortness of breath, headache, unstable tachycardia and anaphylactic shock - life-threatening conditions that require urgent medical attention.
Both intolerance and allergy to milk and dairy products can be identified quickly and easily with hospital tests. If one of the two conditions is suspected, it is advisable to consult a personal physician and accurately diagnose one of the two conditions.