Probiotics are live bacteria that help support your digestive system. Your body is full of bacteria, both good and bad and probiotics are described as good bacteria because they help keep your stomach and digestive system healthy.
Probiotics are naturally found in your body and you can also find them in some foods and supplements.
Medical professionals often suggest probiotics or a cultured yoghurt to help with digestive problems and complications and as antibiotics cannot distinguish between good and bad stomach bacteria, taken a probiotic during or after a course of antibiotics is recommended.  
The two most common probiotic strains are, 
Lactobacillus. - You’ll find in yogurt and other fermented foods. Different strains can help with diarrhoea and may help with people who can’t digest lactose, the sugar in milk.
Bifidobacterium  - You can also find it in dairy products and it may help ease the symptoms of irritable bowel syndrome (IBS).