What is Acidophilus?

Acidophilus is a species of probiotic bacteria within the Lactobacillus genus. There are many different strains (types) within this species, including Lactobacillus acidophilus NCFM®. Find out everything you need to know about this important species of probiotic bacteria and its benefits 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 can be found in the following Optibac supplements:

Other Optibac Lactobacillus acidophilus strains include Rosell-52, which can be found these products:

 Lactobacillus acidophilus La-05®, and Lactobacillus acidophilus La-14®  strains can be found in this Optibac supplement:

Key takeaway:

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 the best L. 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 some research.

Probiotics come in different ‘formats’: you can choose from acidophilus powders, acidophilus tablets, acidophilus capsules and even acidophilus in liquid format. It's best to choose a format which you will find easy to take, as otherwise you might give up taking them. The majority of products on the market are in capsule format, as these are generally found to be easier to swallow than tablets. Capsules and powders in sachets tend to have better shelf-stability and lower risk of contamination than loose powders or liquids.

Some manufacturers of probioticss use enterically coated capsules to protect the bacteria from the harsh stomach acid. Optibac use robust strains of probiotic that survive to reach the gut without enteric coating. This means our acidophilus capsules can be opened, and the contents sprinkled on to cool, non-acidic food or drinks, and you can still be sure that the bacteria will survive and you are getting the full dose2. You may like to read the following FAQ: Can I open live cultures capsules?

Here are some key tips to ensure that your chosen supplement is of high quality:

  • It should have sufficient scientific evidence to support its safety and ability to survive in the gut.
  • 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.
  • 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).
  • Look at the areas and groups of people in which the strains have been researched, and choose strains which seem most appropriate for you.
  • Make sure your supplement is easy to take. If you choose highly researched probiotics in capsules or tablets then they won't need the protection of the capsule, and you'll be able to chew them or open them and take the contents alone if that's easier for you. 

Key takeaway:

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.

dailies image
Optibac Every Day MAX contains Lactobacillus acidophilus strains

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 criteria2.

What is L. acidophilus used for?

This species is so-called because it is made up of lactic acid-producing bacteria. One shared preference for all these strains is that 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 intolerances1.

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. These 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. 

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. This is described in more detail later on in this article.

Key takeaway:

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

How much acidophilus should I take?

This question is a little tricky to answer, as different health symptoms require not only different strains, but potentially different dosages. As a general rule, we would advise following the clinical trial data, taking as close to the same daily dosage that was used in the trial as you can. Wherever possible Optibac probiotics are formulated in this way too, using data and dosage information from the most significant clinical trials. Remember that everyone has a unique gut microbiome, and different strengths suit different people. You may need to try a couple of different supplements before finding the one which suits you best, though allow a week or two for the microbiome to adjust when you first start to take a new supplement.

Key takeaway:

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. Experiment until you find the dosage that suits you best.

Is it ok to take L. acidophilus every day?

This is a common concern, but people have been consuming probiotics daily in a variety of fermented foods and drinks for hundreds of years. In the majority of research studies using probiotics, participants are typically given a daily supplement of probiotics3. Some supplements, such as One Week Flat, are designed to be taken as a short course as and when desired, but many people find they get on better when they take a probiotic supplement every day. There's no evidence that doing this will cause dependency or 'overdose', and daily consumption of good bacteria is generally considered to be of benefit.

  • Key takeaway: It's fine, and often desirable, to take your favourite probiotic every day. Read more about taking probiotic bacteria every day over on the Probiotics Learning Lab.

Are there any side effects from taking acidophilus?

In general probiotics, including those from the acidophilus species, are consdiered to be extremely safe4, and have very few side effects. The majority of people do not experience any negative symptoms from taking probiotic supplements. 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 digestive 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, stop taking the product and contact 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 takeaway:

Side effects from probiotics are very unusual. Occasionally, mild abdominal discomfort and/or bloating may occur 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 L. acidophilus take to work?

This is a question that is often ansked, but frustratingly there is no ‘one size fits all’ answer here! 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 probiotic 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 takeaway:

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.

You should now be fully informed about all aspects of L. acidophilus, so can go ahead and shop for your ideal acidophilus now.

You may also like to read: What is Lactobacillus?

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. 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.
  2. Mai, V., et al. (2017) ‘Novel encapsulation improves recovery of probiotic strains in fecal samples of human volunteers’. Appl Microbiol Biotechnol, 101(4):1419-1425.
  3. Iannitti, T. and Palmieri, B. (2010). Therapeutical use of probiotic formulations in clinical practice. Clinical Nutrition, 29(6): 701-725.
  4. Morovic, W., et al. (2017) ‘Safety evaluation of HOWARU® Restore (Lactobacillus acidophilus NCFM®, Lactobacillus paracasei Lpc-37, Bifidobacterium animalis subsp. lactis Bl-04 and B. lactis Bi-07) for antibiotic resistance, genomic risk factors, and acute toxicity’. Food Chem Toxicol, 110:316-324.