Is it safe to keep milk in its original plastic jug for a week?
Yes for food safety if it stays cold and in date. For lower plastic contact, use glass when it is easy.
What's actually in it
Most gallon milk jugs are HDPE plastic. They are made for refrigerated milk and are widely used. Keeping milk in the original jug for a week is mainly a food-safety question: is it cold, within date, and handled cleanly?
The plastic-contact question is separate. Milk contains fat, and the jug touches the milk every day until it is empty. That does not make one jug an emergency. It does make glass a better routine choice when it is easy.
What the research says
FDA food-safety guidance says milk and milk products should be kept refrigerated at 40 degrees F or below and used by the product date.
A 2025 study in J Hazard Mater found plasticizers in 85% of analyzed foods and reported that exposure varied by food type, packaging, and population group.
A 2025 study in Environ Monit Assess found microplastics in analyzed milk packaging samples and said contamination may happen during manufacturing or packaging.
If your family drinks milk quickly, the original jug is a reasonable convenience. For a lower-plastic routine, buy glass-bottled milk where available or pour 1 to 2 days of milk into a clean glass jar. Do not transfer milk into a dirty or warm container.