Lactose intolerance and milk allergies are very common but remain underestimated. If you have lactose intolerance, you're not alone. The underlying problem is a lack of lactase - an enzyme produced by your small intestine, which breaks down lactose in preparation for absorption into your bloodstream. Lactase deficiency leads to problems in breaking down and absorbing milk sugar (lactose malabsorption).

Some people who believe they are lactose intolerant actually don't have impaired lactose digestion. And not everyone with low levels of lactase is lactose intolerant. Only people with low lactase levels and symptoms are considered lactose intolerant.

In addition, intolerance to a food isn't the same as a food allergy. Lactose intolerance doesn't involve your immune system and doesn't necessarily require complete avoidance of milk products. You can control symptoms of lactose intolerance through a carefully chosen diet that limits lactose without cutting out calcium.

• Calcium (Calcium citrate)
• Calcium Gluconate)
• Diarrhea
• Food allergy

Symptoms are usually mild, but may sometimes be severe. The severity of symptoms doesn't seem to correlate with the degree of lactose malabsorption. Instead, symptoms seem to be related to a range of factors, including ethnicity, age and digestion rates.

Lactose intolerance isn't easily diagnosed by signs and symptoms alone. Many other conditions, including stomach flu and irritable bowel syndrome, can give you similar symptoms. In young children, diarrhea may also be a sign of milk protein allergy, along with eczema, irritability and poor weight gain.

Causes 

The cells that line your small intestine produce an enzyme called lactase. This enzyme is responsible for breaking down lactose into two simple sugars — glucose and galactose — that can be absorbed into your bloodstream. A lack of lactase prevents lactose from being broken down, causing the symptoms of lactose intolerance.

There are three types of lactose intolerance, based on the cause:

• Primary lactose intolerance. Normally, your body produces large amounts of lactase at birth and in early childhood, when milk is the primary source of nutrition. However, like all mammals, most people experience a decrease in lactase production after weaning. This gradual decline causes many adults to experience symptoms of lactose intolerance.

• Secondary lactose intolerance. This form of lactose intolerance occurs when your small intestine decreases lactase production after an illness, operation or injury to your small intestine. It can occur as a result of intestinal diseases such as celiac disease, gastroenteritis or inflammatory bowel disease, especially Crohn's disease. This type of lactose intolerance can last only a few weeks and be completely reversible. However, if it's caused by a long-term illness, it may be permanent.

• Congenital lactose intolerance. It's possible for babies to be born with lactose intolerance. This rare disorder is passed from generation to generation in a pattern of inheritance called autosomal recessive. This means that both the mother and the father must pass on the defective form of the gene for a child to be affected. Infants with congenital lactose intolerance are intolerant of the lactose in their mothers' milk and have diarrhea from birth. The disorder was usually fatal before the introduction of lactose-free infant formulas.