Breast milk can safely stay out at room temperature (77°F or 25°C or below) for up to 4 hours, according to the CDC and other health authorities

. Some sources suggest that at cooler room temperatures (around 25°C or lower), breast milk may remain stable for up to 6 hours, but it is best to refrigerate it within 4 hours to maintain quality and safety

. If the room temperature is warmer, especially above 29°C (85°F), breast milk should not be left out for more than 2 hours due to increased risk of bacterial growth

. Additional key points on breast milk storage times:

• In the refrigerator (at 4°C or 39°F or colder), freshly expressed breast milk can be stored for up to 4 days, with some guidelines allowing up to 5-7 days if stored properly at the back of the fridge

• In the freezer (at -18°C or 0°F or colder), breast milk can be stored for about 6 months optimally, and up to 12 months is acceptable for quality

• Once thawed, previously frozen breast milk can be kept at room temperature for 1 to 2 hours and in the refrigerator for up to 24 hours but should not be refrozen

• Any breast milk left over after a feeding should be discarded if not used within 2 hours to avoid contamination

In summary, freshly expressed breast milk can stay safely out at room temperature for up to 4 hours (sometimes up to 6 hours in cooler conditions), but refrigeration or freezing is recommended as soon as possible to preserve safety and quality