How to Tell if Probiotics Are Still Alive?

October 10, 2025 •

4 min read

Over 7 million Americans use probiotics, and knowing if these living microorganisms are still viable is crucial for reaping their potential benefits. A probiotic's effectiveness is directly tied to the number of live, active cultures it contains, which can diminish over time due to improper storage or manufacturing.

Quick Summary

Assessing probiotic viability involves checking storage conditions, expiration dates, and physical changes. While lab testing is required for definitive results, following best practices helps ensure potency. Learn about factors impacting shelf-life, at-home test misconceptions, and proper supplement storage.

Key Points

Storage is Key: Always follow the label's storage instructions, as heat, light, and moisture kill off live probiotic cultures.
Check Expiration Dates: The manufacturer's date guarantees potency; effectiveness declines significantly after it passes.
Rely on Label Claims: Choose products that guarantee a specific CFU count at the time of expiration, not just at the time of manufacture.
Discard if Compromised: If you notice a strange smell, clumping, or container damage, the probiotic has likely lost its viability.
Monitor Your Body: A lack of symptom improvement after consistent use may indicate an ineffective or non-viable probiotic.
Avoid Unreliable Tests: DIY methods like the 'milk test' are not accurate for determining probiotic viability and can be misleading.

Understanding the Fundamentals of Probiotic Viability

For a probiotic to provide health benefits, the living microorganisms must survive manufacturing, storage, and the digestive tract. Viability is measured in Colony Forming Units (CFU), a count that indicates the number of active, beneficial bacteria. Several factors can compromise these live cultures, including heat, light, moisture, and the type of probiotic strain. Proper handling and storage are the most critical steps to preserve the potency of a supplement.

The Limitations of DIY and Sensory Tests

No simple at-home test can accurately determine the CFU count or survival rate of all probiotic strains. The popular 'milk test' is often debunked because it only works for specific strains of lactobacillus and not other common probiotic bacteria like bifidobacterium. Curdling milk in this test doesn't guarantee the product contains an effective dose of live, viable cultures.

Why At-Home Tests Are Unreliable

Strain Specificity: Not all probiotic strains behave the same way. Some don't ferment lactose, rendering the milk test useless.
Contamination: A home environment is not sterile, meaning unintended bacteria could cause the milk to curdle, leading to a false positive.
Inaccurate Quantification: Even if a test indicates some bacterial activity, it cannot measure the concentration or therapeutic dose of the probiotic.
Professional Lab Equipment: The gold standard for assessing viability is through specialized, culture-dependent or independent lab testing, a process not accessible to consumers.

Reliable Indicators of Probiotic Potency

Since at-home tests are unreliable, consumers must rely on a combination of labeling, storage practices, and physical observations to infer a product's viability. The following indicators offer the best clues to a probiotic's condition.

The Label is Your Best Guide

Guaranteed CFU Count: Look for products that guarantee a specific CFU count at the time of expiration, not just at the time of manufacture. This is a sign of a reputable manufacturer that uses stable, well-protected strains.
Expiration Date: The manufacturer's expiration date is the most reliable timeline for guaranteed potency. Beyond this date, the viability of the bacteria begins to decline significantly.
Storage Instructions: The label will specify if the product is shelf-stable or requires refrigeration. Adhering to these instructions is paramount.

Signs of Compromised Probiotics

Sometimes, even if a product isn't expired, improper handling can render it ineffective. Check for the following physical signs of degradation:

Unusual Smell: A strange or sour smell could indicate spoilage or a compromised seal.
Clumping or Damage: For capsules or powders, moisture exposure can cause clumping. A damaged container or broken seal is also a red flag.
Loss of Expected Benefits: The most practical test is to monitor your body's response. If you've been taking a probiotic consistently and see no improvement in digestive symptoms, the cultures may have lost their potency.

Best Practices for Maintaining Probiotic Viability

Proper storage is the most important way to ensure the live cultures in your supplements remain active. The specific requirements vary depending on the product, so always check the label.

Comparison Table: Refrigerated vs. Shelf-Stable Probiotics


Feature	Refrigerated Probiotics	Shelf-Stable Probiotics
Strains	Often contain more fragile strains that are sensitive to heat and moisture.	Made with hardier, more resilient strains or are freeze-dried.
Storage	Must be kept in a cold environment (e.g., 2°C to 8°C or 36°F to 46°F) to remain viable.	Can be stored at cool, controlled room temperatures (typically below 25°C or 77°F).
Packaging	Usually in moisture-proof, opaque containers. Some use technologies like Activ-Vial™.	Often packaged in specialized, moisture-resistant sachets or airtight bottles.
Convenience	Less convenient for travel or busy lifestyles due to constant cooling needs.	Highly convenient for travel and daily routines, as they don't require refrigeration.
Considerations	The cooling chain must be maintained from manufacturing to your home.	Can still be negatively affected by high heat and humidity if stored improperly.

Proper Storage Tips

Follow the Label: Some products absolutely require refrigeration, while others are designed to be stable at room temperature.
Keep Away from Heat and Humidity: Never store probiotics in a hot car, bathroom cabinet, or near a window sill.
Use Original Packaging: The manufacturer's packaging is designed to protect the cultures. Avoid transferring capsules to a weekly pillbox.
Minimize Exposure: Open the bottle only when needed and reseal it tightly to minimize exposure to air and moisture.

Conclusion

While you cannot definitively tell if probiotics are still alive without professional lab testing, you can make an educated assessment by observing key indicators. Prioritizing proper storage according to the label's instructions is the most crucial step for maintaining potency. Additionally, paying close attention to the product's expiration date, guaranteed CFU count, and any physical changes can help ensure you're consuming a viable, effective supplement. If you notice a decline in the health benefits you typically experience, or if the product has been stored improperly, it's likely time to purchase a fresh bottle.

Authoritative Source

For an in-depth, academic look at probiotic viability testing, you can read the review published in Frontiers in Microbiology on assessing viability and stress tolerance: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.818468/full.

Frequently Asked Questions

While expired probiotics are generally not harmful, their effectiveness is significantly reduced because the number of live microorganisms decreases over time. For optimal results, it is best to use them before the expiration date.

For probiotics that require refrigeration, leaving them out for a prolonged period can kill the live cultures due to exposure to heat and light. Always follow the specific storage instructions on the label.

The most practical indicator is an improvement in the symptoms you are addressing, such as reduced bloating, improved digestion, or increased bowel regularity. If you see no positive change after consistent use, the probiotic may be ineffective.

No, the at-home milk test is not reliable. It only works for a few specific probiotic strains and cannot accurately measure the number of viable cultures. Other bacteria could also cause a false positive, leading to misleading results.

CFU stands for Colony Forming Units, which is a measure of the number of live, active probiotic microorganisms in each serving. Higher CFU counts often indicate a more potent product, but the strain quality is also important.

While proper storage cannot extend a probiotic's shelf life beyond its expiration date, it can prevent the premature degradation of the live cultures. Keeping them in a cool, dark, and dry place is crucial.

Physical signs of a compromised probiotic include an unusual smell, visible clumping or moisture in capsules or powders, or a damaged container or seal. If you observe any of these, it is best to discard the product.