Probiotics are live bacteria and yeasts promoted as having various health benefits. They're usually added to yoghurts or taken as food supplements, and are often described as 'good' or 'friendly' bacteria.
Probiotics are thought to help restore the natural balance of bacteria in your gut (including your stomach and intestines) when it has been disrupted by an illness or treatment.
Probiotics may be helpful in some cases, but there's little evidence to support many health claims made for them. For example, there’s no evidence to suggest that probiotics can help treat eczema.
However, it does seem that for most people probiotics appear to be safe. If you wish to try them – and you have a healthy immune system – they shouldn't cause any unpleasant side effects.
If you're considering trying probiotics, there are a few issues you need to be aware of.
Firstly, probiotics are generally classed as food rather than medicine, which means they don't undergo the rigorous testing that medicines do.
Because of the way probiotics are regulated, we can’t always be sure that:
It's also worth noting that there are many different types of probiotics that may have different effects on the body, and little is known about which types are best. Don't assume the beneficial effects seen with one type are the same as other similar types or will be repeated if used for another purpose.
Lastly, there's likely to be a huge difference between the pharmaceutical-grade probiotics that show promise in clinical trials and the yoghurts and supplements sold in shops.
Read on or use the links below to find out about the evidence concerning some common uses for probiotics:
Without probiotics, antibiotics can sometimes wipe out the protective gut bacteria, resulting in diarrhoea.
Probiotics given with antibiotics may also reduce the risk of developing a Clostridium difficile (C. difficile) infection. C. difficile are potentially dangerous bacteria that can cause diarrhoea and life-threatening complications. They can infect the gut if the balance of gut bacteria is disturbed by antibiotics.
Probiotics are thought to directly kill or inhibit the growth of harmful bacteria, stopping them producing toxic substances that can make you ill.
There's some evidence that probiotics can shorten an episode of diarrhoea caused by a stomach bug by about a day.
However, the evidence isn't yet strong enough to make any treatment recommendations. Read the NHS Choices analysis of research into diarrhoea caused by a stomach bug.
Some babies born prematurely are at risk of a serious condition called necrotising enterocolitis (NEC). This is when tissues in the baby's gut become inflamed and start to die.
There's some good evidence that probiotics may reduce the likelihood of premature babies developing NEC, although there are still some uncertainties, and routine use of probiotics in premature babies isn’t currently recommended.
This is supported by a research published in 2010, although we don't yet know the extent of the benefits, nor the most effective type of probiotic.
Probiotics won't work for everyone with IBS, but if you want to try them, the National Institute for Health and Care Excellence (NICE) suggests taking them for at least four weeks, at a dose recommended by the manufacturer, to see if they help.
Lactose intolerance is a common digestive problem in which the body is unable to digest lactose (a type of sugar found mainly in milk and dairy products).
Some studies have found that certain probiotics, such as Lactobacillus acidophilus, may help to reduce the symptoms of lactose intolerance, which include stomach cramps, flatulence and diarrhoea. Research into this is ongoing.
In the meantime, if you are lactose intolerant, you may wish to try probiotic preparations (not yoghurts) of Lactobacillus acidophilus to see if they help.
Some people with ulcerative colitis need to have part of their bowel removed and a loop of bowel constructed in its place. This loop, or pouch, can sometimes become inflamed, leading to diarrhoea and other problems. This is known as "pouchitis".
Small studies have shown that adding sachets of a probiotic preparation called VSL#3 to drinks or yoghurts can help treat pouchitis. However, more research is needed before it can be recommended as an effective treatment.
It has been suggested that probiotics may be a useful treatment for babies with colic, but there's little evidence to suggest they're effective.
A 2013 study concluded that certain probiotics may help crying infants with colic that are exclusively breastfed. However, generally, it found insufficient evidence that probiotics can help manage colic effectively or prevent infants from crying.
Since then, a small but well-conducted study found that these probiotics had no effect on infant colic in either breastfed or bottle-fed babies.
Read the NHS Choices analysis of this research.
Adverts for probiotic yoghurts used to claim they could "boost your immune system", but these claims were ruled unproven by The European Food Safety Authority and can no longer be made.
There’s a lack of evidence for probiotics benefiting the immune system, and research found that in healthy children, probiotic supplements had no effect on antibody levels, days of fever and number of infections.
There's no reason why you should need to "rebalance" your gut bacteria if you’re already perfectly healthy, despite the claims in some marketing material.
There have been suggestions that probiotics can help in the treatment of bacterial vaginosis. However, even when they are taken with antibiotics, there's currently no evidence of any extra benefits.
The results of research into probiotics for vaginal thrush have been inconsistent and it's not possible to recommend them as a treatment.
Some studies have suggested that giving probiotics to young children may reduce their risk of developing eczema, but the evidence is not very strong.
There's no evidence to support claims that probiotics can help treat symptoms of eczema.
A 2008 review found that probiotics do not reduce eczema symptoms, such as itching, nor do they change the severity of a person's eczema.