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Baby Bottles · Troubleshooting

Baby Bottle Leaking: 6 Causes and Fixes

Everything you need to know about baby bottle leaking: 6 causes and fixes, explained plainly.

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How to fix it

Work through these in order, the most common causes come first.

  1. Start With the Basics

    Vent or valve seating: For any bottle with an internal vent or valve, disassemble it completely and reseat every piece before reattaching the collar. This is the single most common cause of leaking, especially in the first few weeks with a new bottle system. Collar threading: A collar that feels tight but is actually cross-threaded won't create a proper seal.

  2. Diagnosing Your Specific Problem

    Leaking from the collar or where the nipple meets the bottle: almost always a seating or threading issue. Reseat the vent or valve and check the collar is threaded straight, not at an angle. Leaking that started suddenly after months of normal use: points to a worn nipple or vent piece.

  3. See Also

    Brown's Options+ Review - the deepest vent system in this category Philips Avent Natural Review - simpler valve-based alternative Baby Bottle Causing Gas - related troubleshooting

Start With the Basics

Vent or valve seating: For any bottle with an internal vent or valve, disassemble it completely and reseat every piece before reattaching the collar.

This is the single most common cause of leaking, especially in the first few weeks with a new bottle system.

Collar threading: A collar that feels tight but is actually cross-threaded won't create a proper seal.

Unscrew fully and realign it straight before retightening.

Fill level: Overfilling past the marked line, or sealing immediately after adding warm liquid, can build pressure that pushes liquid past the seal.

Diagnosing Your Specific Problem

Leaking from the collar or where the nipple meets the bottle: almost always a seating or threading issue.

Reseat the vent or valve and check the collar is threaded straight, not at an angle.

Leaking that started suddenly after months of normal use: points to a worn nipple or vent piece.

Inspect for cracks, warping, or a loose fit at the base and replace the worn part.

Leaking only when the bottle is tilted or shaken: more common with base or collar valve systems (Philips Avent, Comotomo) than internal straw vents, since these valves generally vent and seal best closer to vertical.

See Also

Brown's Options+ Review - the deepest vent system in this category Philips Avent Natural Review - simpler valve-based alternative Baby Bottle Causing Gas - related troubleshooting

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Answers

Frequently asked questions

Why does my Dr. Brown's bottle leak from the collar?

This is almost always the internal vent not seated correctly. The 2-piece vent, a reservoir and a straw, has to sit properly inside the collar before it's screwed on, or milk can bypass the seal and leak out around the collar threads. Disassemble fully, reseat the vent pieces, and check that the collar threads aren't cross-threaded before tightening.

Is it normal for a new bottle to leak a little at first?

A brand-new bottle shouldn't leak under normal handling once correctly assembled. If a bottle leaks from day one, check that all parts, especially any internal vent pieces, are seated correctly and that the nipple collar is threaded straight, not tightened at an angle. Persistent leaking after correct assembly points to a worn or defective part rather than normal break-in.

Can overfilling a bottle cause leaking?

Filling past the marked fill line, or filling with warm liquid and then sealing immediately, can cause pressure buildup that pushes liquid out around the nipple or collar during handling. Fill to the marked line and let any air displacement settle for a few seconds before fully sealing the collar.

Should I replace a bottle that keeps leaking even after reassembly?

If you've reseated all parts correctly, checked the collar threading, and inspected the nipple and any vent pieces for cracks or warping, and it still leaks, the nipple or vent piece is likely worn or defective and should be replaced. Nipples and vent pieces are generally sold separately and don't require replacing the whole bottle.

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