What is Acidophilus?

Acidophilus is a species of probiotic bacteria, within the Lactobacillus genus. There are many different strains (types) of acidophilus, including Lactobacillus acidophilus NCFM®. Find out more about acidophilus in this FAQ.

When you mention probiotics, acidophilus is often the first name that springs to mind. 'Acidophilus' has become synonymous with the word 'probiotic' and many people just ask for an 'acidophilus supplement' when they're looking for a probiotic. However, it is important to note that acidophilus is just one of many different species of probiotics. It's even more important to understand that within each species of bacteria, there are many different strains, all with unique properties. Read more about the difference between species and strains, or read on to find out everything you need to know about acidophilus probiotics and supplements. 

strain family
Taxonomy diagram

What is acidophilus?

Acidophilus is a species of bacteria from the Lactobacillus genus: its full name is written as Lactobacillus acidophilus, sometimes abbreviated to L. acidophilus. It is a naturally-occurring bacteria found in the gut, mouth and vagina and has been incredibly well-researched in studies focusing on a number of different areas of health. Due to its numerous health benefits L. acidophilus is commonly found in probiotic supplements, such as our own.

Within the acidophilus ‘species’, there are a large number of specific ‘strains’ (types) of bacteria. One example is Lactobacillus acidophilus NCFM®, which is thought to be one of the most widely researched strains of probiotic in the world, and certainly the most extensively researched strain of L. acidophilus.

You can find this strain in our Every Day EXTRA and Every Day MAX. Other L. acidophilus superstars include Lactobacillus acidophilus Rosell-52 (in our Every Day and For travelling abroad), Lactobacillus acidophilus La-05®, and Lactobacillus acidophilus La-14®   (in our Pregnancy).

Key fact:

Acidophilus is a species of bacteria that sits within the Lactobacillus genus. Within the species there are many different individual ‘strains’.

strain image
L. acidophilus under microscope

What is acidophilus used for?

Many of the benefits of a probiotic are dependent on the specific strain used. Only a few characteristics are common to all strains within a species. This section looks at those characteristics that are shared across all bacteria from the Lactobacillus acidophilus species.

Lactobacillus acidophilus is a species of lactic acid-producing bacteria. Once they have colonised the gut, they prefer to use carbohydrates and sugars such as lactose as their fermentation substrate. This means that they break down these sugars as they pass through our intestine, which is why they are often used by those with lactose intolerances. People with lactose intolerance lack sufficient digestive enzymes to digest lactose (a sugar found in milk and dairy products) but strains of L. acidophilus bacteria can help to break lactose down into a more digestible form. L. acidophilus strains produce lactic and acetic acids as a by-product of fermentation. These acids lower the pH of the intestines, discouraging the over-growth of bad bacteria, known as pathogens, and encouraging the growth of ‘friendly’ bacteria, known as probiotics, in the gut. In this way acidophilus is beneficial in maintaining a healthy balance of gut flora.

Beyond these characteristics, which are common to all bacteria within the acidophilus species, most of the known benefits of L. acidophilus are found at ‘strain’ level. For example, Lactobacillus acidophilus NCFM® has very different characteristics and health benefits to Lactobacillus acidophilus La-14®. This is described in more detail later on in this article.

Key fact:

When choosing the best acidophilus supplement for your needs, look at the L. acidophilus strains which have been researched for the specific health condition or symptom you wish to support. 

3 ways Lactobacillus acidophilus can benefit your health

As already mentioned, many of the benefits of Lactobacillus acidophilus are held at individual ‘strain’ level. For example L. acidophilus NCFM is known to reduce occasional abdominal bloating. But, let’s take a look at how their ‘shared’ characteristics can benefit our health:

1. L. acidophilus as a species of bacteria may help to restore the balance of ‘good’ vs ’bad’ bacteria in both the gut and the vagina. They do this by taking up space on the lining of the digestive (or vaginal) tract which effectively prevents ‘bad’ bacteria such as E.coli from colonising and causing symptoms. By competing for both space and nutrients with these unfavourable bacteria, they make it harder for them to over-growand disrupt the healthy balance of gut flora.

2. L. acidophilus as a species are known to secrete certain acids, such as lactic acid. By doing so they are able to lower the pH of the intestines (or vagina), which discourages bad bacteria from proliferating, and maintains a healthy gut (or vaginal) environment.

3. L. acidophilus, along with other probiotic species, are also known to support digestion by producing different digestive enzymes that help us to break down our food more efficiently. This can help with food intolerances such as lactose intolerance and their related symptoms. 

Key fact:

The ability to favourably alter the pH of their external environment, coupled with their ability to produce digestive enzymes and improve makes bacteria from the L. acidophilus species a popular choice for probiotic supplements.

Are all strains of L. acidophilus the same?

To recap, all strains of L. acidophilus are part of the genus (or ‘family’) of lactic-acid-producing bacteria called Lactobacillus.

Species and strains from this genus tend to be the most widely used in probiotic supplements due to their versatile nature. But not all strains have the same properties. For this reason, when looking at supplements, it is best to compare them at strain level, as opposed to merely species or genus level.

Below are some examples of individual strains of L. acidophilus. The unique properties that they each possess dictates how they are best used, and which areas of health they best support:

  • Gut health – many strains of L. acidophilus have been clinically trialled for their efficacy in supporting various different aspects of gut health. For example, Lactobacillus acidophilus NCFM® has been shown in trials to reduce the pain and bloating associated with IBS1, to reduce diarrhoea2 in children, and to reduce the symptoms associated with lactose intolerance3. Whereas Lactobacillus acidophilus LA-05® has proved effective at alleviating constipation in elderly patients4 (when used alongside another strain: Bifidobacteria lactis BB-12®), and also reducing inflammation and symptoms in ulcerative colitis patients5.
  • Immune support – with 70% of our immune cells being located in the gut, it is not surprising that the health of our gut flora affects immune function. Certain strains of L. acidophilus have been shown to support our immune system, and reduce the likelihood of picking up transmissible infections. In one study6, results indicated that Lactobacillus acidophilus Rosell-52 reduced the incidence of gastric disorders, ear-nose-throat (ENT), or bronchopulmonary infections by 25% in school-age children, thereby reducing the number of school absences by 40%.​Lactobacillus acidophilus NCFM® has also demonstrated its ability to increase circulating antibodies in the blood of healthy adults following vaccination7, and reduce the incidence of cold symptoms, in children8.
  • Mental health – research has shown that the health of the microbiome impacts on our emotional and mental health, and many strains of friendly bacteria have been used in clinical trials to assess their impact on various mood disorders.  Lactobacillus acidophilus Rosell-52 is one of the most researched strains of L. acidophilus for mental health and has shown potential for both anxiety9 and depression10.
  • Antibiotic use – certain strains of bacteria have been trialled for their effectiveness at either reducing the side-effects when taking a course of antibiotics, or rebuilding the health of the microbiome after completing a course. Lactobacillus acidophilus Rosell-52® when taken in conjunction with Lactobacillus rhamnosus Rosell-11 has proven effective against developing antibiotic-associated diarrhoea11.Lactobacillus acidophilus NCFM®, taken in conjunction with Bifidobacterium lactis Bi-07®, has shown its effectiveness at stabilising the gut microbiota following antibiotic treatment12.
  • Vaginal Health – a healthy vaginal microflora is heavily dominated by bacteria from the Lactobacillus genus. Many different species and strains of bacteria from within this genus have been used in clinical trials in an attempt to improve vaginal health parameters.One such strain is: Lactobacillus acidophilus La-14®. When used alongside Lactobacillus rhamnosus HN00113, this strain was seen to significantly reduce vaginal discharge and symptoms of Bacterial Vaginosis (BV).

Key fact:

Different strains within the same species have different modes of action in the body, so it is important to find the strain that is most suitable for your needs.

Healthcare practitioners can find out more about L. acidophilus and the research mentioned above by visiting the Probiotics Database, on the Probiotic Professionals site.

How do I find the best acidophilus probiotic?

This really depends on what is meant by ‘best’! In terms of suitability, it’s a case of finding the right strain to suit you, and your own specific health requirements, which can involve a bit of searching.

However, there are a few key ways to ensure that the supplement in question is of high quality.

  • Firstly, it should have sufficient scientific evidence to support its safety and ability to survive in the gut.
  • Secondly, opt for ‘quality over quantity’. Don’t be drawn in solely by huge billion counts of a supplement. Higher billions do not necessarily equal higher product quality – it’s much more important to get the most researched strains, even if they’re in lower quantities. It’s definitely a case of ‘quality over quantity’ when it comes to probiotic supplements.
  • Lastly, check the product has a 'time of expiry' guarantee as opposed to a 'time of manufacture' guarantee, as this means the product strength is guaranteed until the supplement goes out of date, rather than just at the time of manufacture (as numbers decrease after this point).

Key fact:

Do your homework before buying an L. acidophilus supplement. Choose one containing high quality, well-researched strains which meet your own individual health needs, whilst also satisfying the above quality criteria.

One of the most highly researched strains of acidophilus is Lactobacillus acidophilus NCFM®, which can be found in our supplements Every Day EXTRA and Every Day MAX, both of which satisfy the above mentioned product quality criteria.

Dosage: how much acidophilus should I take?

This question is a little tricky to answer, as different health symptoms require not only different strains of acidophilus, but potentially different acidophilus dosages. As a general rule, I would advise following the clinical trial data as closely as possible. So, if a double-blind, placebo-controlled clinical trial shows efficacy for supporting a condition or symptom that is of relevance to you, I would recommend taking as close to the same daily dosage that was used in the trial as you can. Wherever possible our acidophilus probiotics are formulated in this way too, using data and dosage information from the most efficacious clinical trials.

The probiotic acidophilus is ‘cultured’ or in other words, grown, in a laboratory. The bacteria are then extracted and usually freeze-dried for preservation. Probiotics come in different ‘formats’, and how you prefer to take your daily dose is a personal choice. You can choose from acidophilus powders, acidophilus tablets, acidophilus capsules and even acidophilus in liquid format. The majority of products on the market are in capsule format, as these are generally found to be easier to swallow than tablets, and have better shelf-stability, and less risk of contamination than loose powders (powders portioned in to individual sachets also avoid the risks associated with loose, bottled powders).

Some manufacturers of probiotics use enterically coated capsules, which are said to protect the bacteria inside them from the harsh acidic conditions of the stomach. We, however, use robust strains of friendly bacteria that are known to survive at a low pH anyway, so we have no need for enteric coating. This means that our capsules can be opened, and the contents sprinkled on to food or drinks (so long as they are not hot or too acidic) with no loss to product integrity. Even if you open up our acidophilus capsule in this way, you can still be sure that the bacteria will survive and you are getting the full dose. You may like to read the following FAQ: Can I open probiotic capsules?

Key fact:

Different health conditions may require different probiotic doses, so where possible take a supplement which contains a similar CFU (billions) count to that which has been used in clinical trials relating to your specific health issues.

Are there any side effects from taking acidophilus?

Having addressed the topic of acidophilus benefits, it is important to address this frequently asked question. In general probiotics, including those from the acidophilus species, have very few side effects. The majority of people do not experience any negative symptoms from taking an acidophilus supplement. However, everybody is different, and therefore everyone reacts to things differently.

With the introduction of any new probiotic supplement, some people may initially experience mild digestive symptoms, such as: bloating or excess gas. In most cases these symptoms do not last for longer than a few days, and are simply the result of a shift in microbial population and diversity. Mild acidophilus side-effects can simply be a sign that changes are taking place within the eco-system of the gut.

Whilst mild symptoms may be bothersome, they are for the most part, a positive sign that the ‘friendly’ bacteria are doing their ‘job’, crowding out pathogenic strains of bacteria and competing for space on the gut wall lining.

However, if any side effect becomes troubling, or lasts for longer than described, I would always recommend stopping taking the product and contacting the manufacturer for advice. It could be other ingredients in the product that are causing issues, such as a prebiotic fibre. Or, it could just be that the strain of acidophilus is not compatible with your individual microbiome at that time. Always listen to your own body, and respect its uniqueness.

Key fact:

L. acidophilus may occasionally cause mild abdominal discomfort and/or bloating in some people, but this typically only lasts for a few days and indicates that the bacteria have reached the gut. If symptoms persist speak to the manufacturer for advice.

Read our FAQ ‘Do live cultures have side effects?’ to find out more.

How long does acidophilus take to work?

This is a question that often crops up, but frustratingly there is no ‘one size fits all’ answer here either! With everyone’s microbiome being as unique to them as their fingerprint, it is impossible to know for certain how long it will take to feel the benefits of taking acidophilus supplements.

We receive wonderful feedback and product reviews from our customers. For some people our supplements have an almost instant effect, whereas for others it can take several weeks or more. It depends partly on the state of a persons’ health to start with and also their compliance with taking the product. Diet, lifestyle and any medications being taken are other factors to consider. In general, I would advise patience. The benefits are well worth it, and your health will thank you for it in the longer term.

Key fact:

Everybody responds differently, and at different speeds, when starting a new probiotic supplement. Don’t be disappointed if results take a little while, they will be worth it in the longer term.

Shop for acidophilus.

You may also like to read: What is L. helveticus?

For further research in to L. acidophilus and specific strains within this species healthcare professionals might like to take a look at The Probiotics Database.

Authors: Dr Kate Stephens PhD Food and Microbial Sciences; Gut Microbiology (University of Reading), BSc Medical Microbiology

Reviewed by: Dr Aisling Dwyer MB BCh BAO (Medicine, Surgery and Obstetrics), MSc (Personalised Nutrition)​


  1. Lyra, A. et al., (2016) ‘Irritable bowel syndrome symptom severity improves equally with probiotic and placebo’. World Journal of Gastroenterology. 22 (48):10631–10642.
  2. Ruiz-Palacios G. et al., (1996). ‘Feeding of a probiotic for the prevention of community acquired diarrhea in young Mexican children’. Pediatric Research, 39 (Pt. 2):104, Abstr. 1089.
  3. Montes, R.G. et al., (1995). ‘Effect of Milks Inoculated with Lactobacillus acidophilus or a Yogurt Starter Culture in Lactose-Maldigesting Children’. Journal of Dairy Science. 78(8): 1657 – 1664.
  4. Alm L, et al., (1993) ‘Effect of a new fermented milk product "CULTURA" on constipation in geriatric patients. 1st Lactic Acid Bacteria Computer Conference Proceedings’. Horizon Scientific Press, Norfolk, England 1993.
  5. Laake K.O., et al. (2005). ‘Outcome of four weeks intervention with probiotics on symptoms and endoscopic appearance after surgical reconstruction with a J-configurated ileal-pouch-anal-anastomosis in ulcerative colitis’. Scandinavian Journal of Gastroenterology (40):43-51.
  6. Cazzola M. et al., (2010) ‘Efficacy of a synbiotic supplementation in the prevention of common diseases in children: a randomized, double-blind, placebo-controlled pilot study’ Therapeutic Advances in Respiratory Disease, 0(0):1-8.
  7. Paineau D. et al., (2008). ‘Effects of seven potential probiotic strains on specific immune responses in healthy adults: a double-blind, randomised, controlled trial’. FEMS Immunology and Medical Microbiology, 53(1):107-13.
  8. Leyer, G.J., et al., (2009). ‘Probiotic Effects on Cold and Influenza-Like Symptom Incidence and Duration in Children’. Pediatrics; 124 (2): 172-179.
  9. Messaoudi M. et al., (2011), ‘Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects’. British Journal of Nutrition, 105(5):755.
  10. Wallace C. et al., (2017), Findings presented at 13th World Congress of Biological Psychiatry. Poster P-05-015, presented June 19, 2017.
  11. Evans M. et al., (2016), ‘Effectiveness of Lactobacillus helveticus and Lactobacillus rhamnosus for the management of antibiotic-associated diarrhoea in healthy adults: a randomised, double-blind, placebo-controlled trial’. British Journal of Nutrition, 16(1):94-103.
  12. Forssten, S., et al., (2014). ‘Influence of a probiotic mixture on antibiotic induced microbiota disturbances’. World Journal of Gastroenterology, 20(33):11878-85.
  13. Russo R et al. (2018). Evidence-based mixture containing Lactobacillus strains and lactoferrin to prevent recurrent bacterial vaginosis: a double blind, placebo controlled, randomised clinical trial. Beneficial Microbes, Published online ahead of print on December 10, 2018.