There are a few key reasons why prepared formula can go bad and become unsafe to drink after sitting out for more than 1 hour. The main concerns with old formula are bacterial growth and loss of nutrients. Here’s a quick overview of why you should discard formula left out too long:
Bacterial Contamination
Prepared infant formula is the perfect breeding ground for bacteria. Formula provides nutrients that allow bacteria like E. coli, Salmonella, and Cronobacter sakazakii to rapidly multiply to dangerous levels. Bacteria levels can double every 20 minutes. Within an hour at room temperature, bacteria levels can become high enough to make a baby sick. Some of the harmful bacteria that can grow in old formula include:
- E. coli – Can cause diarrhea, UTIs, respiratory illness
- Salmonella – Causes fever, diarrhea, dehydration
- Cronobacter sakazakii – Rare but can cause blood infections, meningitis
An infant’s immune system is not yet mature enough to fight off these bacterial infections. Drinking contaminated formula puts them at risk of developing a serious, even life-threatening, illness. While healthy adults may be able to consume formula with some bacterial growth and only suffer temporary symptoms, it can make babies very sick. Consuming formula left out too long significantly increases an infant’s risk of a dangerous foodborne illness.
Nutrient Loss
Infant formula contains nutrients like proteins, carbohydrates, vitamins, and minerals that infants need to grow and develop. When prepared formula is left out at room temperature for more than an hour, these nutrients start to break down:
- Protein levels decline – Necessary for growth and development
- Carbohydrates break down – Provides calories/energy for babies
- Vitamin C degrades – Boosts immunity and iron absorption
- Vitamin A depletes – Important for eyesight and growth
- Iron reacts with formula – Reduces iron absorbed by infant
Even refrigeration can’t stop the nutrient loss if formula sits longer than 24 hours. The overall nutritional quality of the formula deteriorates the longer it sits at room temperature. Drinking formula past the 1 hour timeframe means babies do not get the full, necessary nutrient profile to help them grow healthy and strong.
How Rapidly Does Formula Go Bad?
Exactly how long does it take before formula becomes unsafe to drink after it is prepared? Here is a breakdown of how soon harmful bacteria can multiply and nutrients decline at different temperatures:
Room Temperature – 72-78°F (22-25°C)
- < 1 hour - Formula still safe if immediately refrigerated
- 1-2 hours – Bacteria can multiply to unsafe levels
- 3-4 hours – Up to 100x increase in bacteria growth
- 6+ hours – Vital nutrients depleted, high bacteria levels
Outdoors in Warm Weather – Above 90°F (32°C)
- Less than 1 hour – Bacteria grows rapidly
- 1 hour – Potentially dangerous levels of bacteria
- 2 hours – Extremely unsafe bacterial contamination
Refrigerator – 40°F (4°C)
- 24 hours – Nutrient loss occurs but bacteria limited
- 48 hours – Increased risk of bacterial growth
- 72+ hours – Stored formula should be discarded
As you can see, temperature plays a big role in how quickly harmful bacteria multiply in infant formula. However, one hour at room temperature is the absolute maximum time limit before prepared formula becomes unsafe.
Safe Formula Handling Tips
To avoid the risks of bacterial contamination and nutrient loss, it’s essential to follow safe formula handling guidelines:
- Discard any prepared formula left out at room temperature for over 1 hour
- Immediately store formula in the refrigerator after preparation
- When feeding baby, use formula within 1 hour of removing from fridge
- Never save unfinished formula bottles to reuse later
- Always follow instructions for proper mixing ratios
- Do not add cereal or other ingredients to formula
- Clean all bottles, nipples, and preparation equipment thoroughly
Adhering to these safe practices reduces the risk of babies developing an illness from spoiled formula. Be sure to follow manufacturer storage instructions and never take risks with old, possibly contaminated formula.
Can You Reheat Formula After an Hour?
It is not recommended to reheat baby formula that has been left out unrefrigerated for over an hour. While reheating formula does kill some bacteria, it does not destroy the toxins they produce. These toxins can continue to make your baby ill even if the bacteria are dead. Reheating may also break down more nutrients in the formula.
The only exception is formula that has just finished being heated and needs to be reheated because the baby did not finish their feeding. In that case, the formula has not been sitting at room temperature for more than an hour and likely has not spoilt.
However, that leftover formula should be discarded within 1 hour after the initial heating. Do not reheat again after that time. It is always safest to make fresh bottles of formula for each feeding by following the manufacturer’s mixing instructions.
Does Smelling Formula Detect Spoilage?
Relying on smell or taste alone is not a reliable way to determine if formula has spoiled after sitting out. Dangerous bacteria like E. coli and Salmonella do not produce odors or flavors that are distinguishable from freshly made formula.
The only foolproof way to know if formula is still safe is by knowing how long it has been left out at room temperature. Trust the 1 hour rule, not your senses. Formula can harbor dangerous levels of bacteria with no noticeable smell or odd appearance.
Can You Add Water to Old Formula?
It is not recommended to top off refrigerated formula that is near the 24 hour storage limit by adding extra water. This can throw off the nutritional ratios and lead to a diluted, imbalanced formula. The added water may also introduce new bacteria to the stored formula.
Likewise, adding powdered formula to water that has been sitting at room temperature for over an hour is also risky. The bacteria levels in the water are unknown and could contaminate the formula.
In both cases, it is safest to discard formula that is near or past its refrigerated shelf life and make a fresh bottle using properly measured, clean water.
Does Boiling Old Formula Make It Safe?
Boiling formula that has been left out for over an hour is not guaranteed to make it safe for consumption. While boiling does kill most bacteria, it cannot remove the dangerous toxins already produced by the bacteria in old formula. The heat from boiling can also further degrade the formula’s nutrients.
Boiling also does not restore formula that was not properly refrigerated or was stored too long back to a safe, nutritious state. Once formula is left out too long at room temperature, it must be discarded. Do not rely on boiling old formula to make it usable again.
Can You Save and Freeze Formula for Later?
Freezing infant formula is generally not recommended, according to the FDA. Formula can separate and lose its nutritional balance during freezing. The frozen state also does not prevent bacterial growth over an extended period.
However, prepared formula can be safely frozen for up to 24 hours if necessary. Make sure to rapidly freeze it right after preparation and keep frozen until ready to thaw and use. Previously frozen formula must be consumed within 1 hour after thawing.
Only freeze formula in a pinch, not routinely. And never save, refrigerate, or freeze formula that has already been partially consumed by baby.
Does Formula Expire After Opening?
Dry infant formula powder usually has an expiration date 6-12 months after the container is opened. This shelf life accounts for loss of nutrients as the formula ages. However, as long as the powder is kept dry in the original container, it is generally considered safe to consume up to 3 months past that printed expiration date.
On the other hand, concentrated liquid formula typically expires within one month after opening. Powdered and liquid formula also expire within 1-2 days of mixing with water. To maximize freshness and nutrition, only make enough formula for each feeding as needed.
When to Throw Out All Formula
In addition to discarding formula left out for over an hour or stored too long, you should also immediately throw out all formula in the following cases:
- You notice any changes in color, smell, consistency
- There are visible signs of spoilage – clumping, separation, sliminess
- Prepared with potentially contaminated water
- Stored improperly at the wrong temperature
- Your baby drank from the bottle and backwashed into it
- There is any chance the formula was tampered with or poisoned
Err on the side of caution and do not take risks with formula you have any suspicion has been compromised. When in doubt, throw it out and mix a fresh bottle.
Conclusion
Infant formula becomes unsafe quite quickly after preparation due to the potential for rapid bacterial growth and nutrient breakdown. Leaving prepared formula unrefrigerated for longer than 1 hour provides a prime opportunity for bacteria to multiply to dangerous levels that can make babies sick. Reheating, freezing, or boiling old formula does not make it safe to serve again. When handling prepared formula, follow the 1 hour rule – if it has been out over an hour, throw it out and make a new bottle.
