Probiotics are live microorganisms that, when consumed in adequate amounts, confer a health benefit to the host, primarily by supporting the balance of the gut microbiome. For these beneficial bacteria to function as intended, their viability, meaning the number of living cells, must be maintained until they reach the body. The manufacturer’s storage instructions, particularly the requirement for refrigeration, are therefore essential for preserving the product’s function. Understanding what happens when this storage is ignored reveals the fate of the live cultures and the resulting loss of potential health benefits.
The Science of Probiotic Degradation
The necessity of refrigeration for certain probiotic supplements stems from the fact that these bacteria are living organisms highly sensitive to temperature fluctuations. Refrigeration, typically between 35°F and 45°F (2°C to 7°C), keeps the bacteria in a dormant or low-metabolic state. This cold environment effectively slows down the speed at which the organisms consume their internal resources, extending their lifespan.
When a refrigerated probiotic is left at room temperature or exposed to heat, the opposite occurs; the elevated temperature significantly increases the bacteria’s metabolic rate. They become more active, rapidly depleting their limited food supply and protective nutrients within the supplement. This accelerated activity leads to a much faster rate of death, or loss of viability. Heat is the primary environmental enemy, with temperatures above 70°F (21°C) causing probiotic bacteria to begin dying off and temperatures above 120°F (49°C) causing rapid cell death.
The Result: Diminished Potency
The practical consequence of this biological degradation is a significant drop in the supplement’s potency, which is measured by Colony-Forming Units (CFUs). The CFU count represents the number of viable, living microorganisms present in the product, and only these live bacteria can colonize the gut and provide the advertised health benefits. A probiotic label guarantees a specific CFU count, but this guarantee is conditional upon the product being stored correctly until the expiration date.
When refrigerated probiotics are not kept cold, the live culture count plummets long before the expiration date, meaning the dose delivered to the consumer is insufficient. For example, a supplement promising 50 billion CFUs may only deliver a fraction of that amount if stored improperly. This reduction in live cultures means the product fails to meet the minimum threshold required to exert a therapeutic effect, rendering the supplement functionally ineffective.
Addressing Safety: Are They Harmful?
A common concern is whether consuming an unrefrigerated probiotic that requires cold storage can be harmful or toxic. Generally, the answer is that the product is more likely to be ineffective than dangerous. The probiotic bacteria that die off due to heat exposure do not typically transform into harmful pathogens or produce toxic compounds. The supplement essentially becomes a capsule of dead or inactive bacterial matter, which the body simply passes through.
However, the risk of general spoilage, similar to any food product, exists if the supplement is exposed to extreme conditions like high heat and humidity for prolonged periods. Excessive moisture can reactivate freeze-dried cultures, leading to degradation and potentially creating an environment where non-probiotic contaminants like mold or other microorganisms could grow. For professionally packaged supplements, this contamination risk is rare, and the primary safety concern remains the loss of efficacy rather than toxicity. If the product looks or smells visibly spoiled, it should be discarded.
Understanding Shelf-Stable vs. Refrigerated Strains
The need for refrigeration is not universal, as the stability of a probiotic supplement depends heavily on the specific strains selected and the manufacturing process. Products labeled as “shelf-stable” are engineered to maintain the viability of their cultures at room temperature. This stability is often achieved by using naturally hardy strains, such as the yeast Saccharomyces boulardii, or spore-forming bacteria like Bacillus coagulans and Bacillus subtilis.
Another key technique is lyophilization, or freeze-drying, which puts the microorganisms into a dormant state, combined with packaging that includes robust moisture barriers. These specialized products can withstand typical ambient temperatures, making them convenient for travel and daily use.
Consumers should always check the label for storage instructions. If a product was purchased from a refrigerated section or explicitly states “Keep Refrigerated,” it contains more temperature-sensitive strains and must be kept cold to ensure its potency.