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?

Yes. 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.

Baby Bottle Leaking: 6 Causes and Fixes

A leaking baby bottle is almost always an assembly or wear issue rather than a defective bottle. We cover the 6 most common causes of bottle leaks, from vent misassembly to a worn nipple, and how to fix each one.

Step-by-Step Guide

Fix 1: Reseat the vent or valve correctly

For vented bottles like Dr. Brown's, disassemble fully and reseat the internal reservoir and straw before reattaching the collar. For valve-based bottles like Philips Avent or Comotomo, confirm the valve is inserted the correct way and fully seated in the collar or base, not sitting at an angle.

Fix 2: Check the collar isn't cross-threaded

A collar that's screwed on at a slight angle instead of straight along the threads will feel like it's tightened but won't create a proper seal. Unscrew fully, realign the collar straight onto the bottle threads, and tighten evenly.

Fix 3: Inspect the nipple for cracks or warping

A nipple that has developed hairline cracks, warping, or a loose fit at the base after months of sterilizing and dishwasher cycles can leak even when everything else is assembled correctly. Hold it up to light and gently stretch the base to check for cracks; replace it if you find any.

Fix 4: Don't overfill past the fill line

Filling above the marked line, or sealing a bottle immediately after adding warm liquid, can build pressure that pushes liquid past the seal. Fill to the line and let a few seconds pass before fully tightening the collar.

Fix 5: Confirm you're using matched parts from the same product line

Mixing a nipple or collar from a different bottle line, even within the same brand, can create a poor seal if the thread designs don't match. Check that all parts are from the same specific product line before assuming a persistent leak is a defect.

Fix 6: Replace worn vent pieces or nipples rather than the whole bottle

If leaking persists after reassembly and inspection, the nipple or an internal vent piece is likely worn out. These are sold separately by every major brand and are the more cost-effective fix versus replacing the entire bottle.

A leaking bottle is one of the most common complaints with any bottle system, and it's almost never a sign of a defective bottle straight out of the box.

Most leaks trace back to assembly, a vent or valve that isn't seated correctly, a collar threaded at a slight angle, or a nipple that's worn from months of sterilizing and dishwasher cycles.

Vented bottles like Dr. Brown's Options+ are more prone to leaking early on simply because there's an extra internal piece that has to seat correctly, not because the design is inherently leakier once you know the routine.

The fixes below start with the most common causes and move toward less frequent ones, so work through them in order.

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.

Leaking from a brand-new bottle on first use: check assembly first. It's more likely a seating mistake than a defect, especially with a multi-piece vented bottle.

Quick Diagnosis

Symptom	Most Likely Cause	Fix
Leaks from collar area	Vent/valve not seated, or cross-threaded collar	Reseat parts; realign collar
Leaks after months of normal use	Worn nipple or vent piece	Inspect and replace worn part
Leaks when tilted	Valve-based design limitation	Hold more upright during feeds
Leaks from a new bottle immediately	Assembly mistake	Recheck vent seating and threading
Leaks from the fill line down	Overfilled or sealed while pressurized	Fill to line, wait before sealing