Probiotics maintain digestive health and comfort by digesting particular substances in the diet and by enabling nutrient absorption. They support immunity by stimulating the body's natural defences and by lining the the intestines with a layer of friendly bacteria that bars harmful substances in the gut from entering the body. The balance of good bacteria can be disrupted by stress, dietary habits, antibiotics and ageing. This can then lead to diarrhoea, excessive gas, bloating, constipation and thrush. Medical studies show that replenishing the intestines with probiotics is a natural way towards maintaining healthy lifestyle. There are different strains of "friendly" bacteria, which have specific beneficial properties and colonise different parts of the intestine. Some products require refrigeration others are temperature stable.