Why Baby Formula Bottles Turn Pink (& How to Get it Out)

Balint Horvath, PhD

Writer, parent, and veteran of baby feeding battles.


Have you recently noticed your baby bottles turning pink after feeding? The breastmilk is a normal color during regular pumping, but a short while after feeding the bottles and leftover milk turn pink. Parents have reported these pink instances with all the popular bottle types including, Avent, Medela, Dr. Brown, and Tommee Tippee. Even parents using traditional plastic bottles have experienced pink bottles. Should you be concerned? 

Baby bottles can turn pink because of a bacterial organism called Serratia marcescens. This pinkish bacteria is found in our environment and can be transmitted from an infected mother’s breast milk. Other causes include poor hand hygiene, improper bottle sterilization, or contaminated water.

Why do baby bottles turn pink?

When baby feeding bottles turn pink, it’s usually a clear indication that there has been some exposure to Serratia marcescens. Since this bacteria can grow anywhere, it might be difficult to narrow down the exact cause. It can be as simple as a contaminated water source or as complex as an infection from the mother. 

Generally, plastic bottles are more susceptible to absorbing this bacteria since plastic generally absorbs odors and bacteria more easily. However, there have been instances where glass bottles also turn pink. 

Why does baby formula turn pink?

It’s unlikely that the baby formula itself is the reason for the contamination. The formula, such as Gerber Gentle or Soothe, goes through extensive testing before it’s packaged. If the formula presents signs of Serratia marcescens, it could be as a result of contaminated water

It could also be as a result of the bottles being cleaned with a towel that has traces of the bacteria on it. If a parent has this bacteria, it can easily be transmitted to towels and utensils used during feeding.

Serratia marcescens – what it is and how to treat it

To understand exactly how Serratia marcescens affects your little one it’s important to know a little more about it.

Serratia marcescens – a microbial culprit?

Serratia marcescens is a bacterial organism that leaves a red-pink hue to the milk it’s been exposed to. The bacteria is activated when the milk stands out at room temperature. Essentially this happens when this opportunistic pathogen makes its way to the baby’s living environment. 

Ordinarily, this bacteria doesn’t affect healthy individuals but since it can be found in water, soil, or even plants, it can end up on your baby’s bottles.

How you can get infected with it

Usually, people most at risk of contracting this bacteria include:

  • People with compromised immune systems or underlying health issues
  • Patients who have been exposed to a course of broad-spectrum antibiotics
  • Patients who have spent an extended period in hospital and had invasive procedures like catheters or feeding tubes
  • New moms might contract the bacteria in the hospital

How babies and bottles get it

This bacteria can easily be transmitted to babies through breast milk. If babies aren’t being fed breast milk, it’s most likely that the baby contracted the bacteria through water or infected kitchen cloths. Anyone with the bacteria could also transmit it to the baby if they don’t practice proper hand hygiene.


For the most part, only a proper medical diagnosis will confirm the presence of the bacteria. There are a few clear symptoms that might indicate the presence of the bacteria:

  • Meningitis
  • Conjunctivitis
  • Pneumonia
  • Sepsis
  • Keratitis
  • Surgical wound infections
  • Bloodstream infections

The good news is, that babies are usually asymptomatic and will usually not get sick from the bacteria. However, it’s still important to remove it from your environment. 

How to treat it

Fortunately, the treatment for Serratia marcescens isn’t overly complex. If you suspect you or your baby may have been exposed to the bacteria, consult your baby’s pediatrician. Other steps to follow include the following:

  • Take the bottles with the pink coloring to the doctor’s appointment.
  • If the mother’s breast milk shows traces, the mom will have to go on a course of antibiotics.
  • Sterilize all baby’s feeding items regularly
  • Everyone who handles the baby and their bottles should practice proper hand hygiene – hands should be washed before handling the baby.
  • If you’re still using the bottles you received from the hospital, it might be a good idea to change to a new brand – check out some of the baby bottles hospitals use, as well as the bottle brands, so you can choose the best brand. 

What to do with bottles that turned pink

The good news is, that the bacteria doesn’t stain your bottles. You also don’t have to chuck them out. Thorough sterilization will be sufficient to remove the bacteria from the bottles while the mom and baby are taking medication if necessary. I’ve included a few easy ways to sterilize the bottles. 


Boiling is sometimes the easiest way to sterilize bottles, loose parts, brushes, and even towels. Plastic bottles should be sterilized more regularly as they tend to absorb bacteria easier than glass bottles. It can be done in a few easy steps:

  • Gather up all the bottles, bottle parts, and bottle brushes and place them in a large pan
  • You can add coarse salt to the water to aid in sterilization
  • Boil the bottles and parts for at least 5 minutes
  • Remove the items using clean tongs and place them on a clean sterilized tray
  • Allow to dry

I’ve included a short clip to show you how easy it is to sterilize bottles on the stovetop. 

Using steam to sterilize it

Another effective way to sterilize your baby bottles and accessories is to use a steam sterilizer. Some units work by being placed in the microwave while others function as stand-alone units. Here you’d have to follow the manufacturer’s specific instructions. As with the boiling option, take the bottles apart and sterilize all components. 

Bleaching it

For parents who use Milton sterilizing agent for their bottles, this option is ideal for you since you’ll already have everything you need. Simply follow these few easy steps:

  • Prepare a Milton/bleach solution in a clean washbasin or small bucket
  • If you’re using Milton, prepare according to instructions, whereas if you’re using bleach, use 2 teaspoons per gallon
  • Place all the bottle parts and brushes in the washbasin and ensure they are completely submerged
  • Manually squeeze the bleach solution through the nipple holes 
  • Soak items for at least 5 minutes – longer if the items haven’t been sterilized in a while
  • Remove the items with clean tongs
  • Make sure not to dry with any towels that could have bacteria on

Here’s a separate article I wrote if you want to learn more about bleaching baby bottles.

Using a dishwasher

For the dishwashing option, you can either use the regular hot water and the drying cycle. Alternatively, if your dishwasher has the “sanitize” feature, make use of that option to ensure the water gets hot enough to kill the bacteria. If you’re using a dishwasher basket, you can place the bottle and accessories in there to sterilize. A portable or countertop dishwasher is also an ideal option to sterilize bottles.


No one wants their baby to be sick and the thought of harmful bacteria lurking in your home can be very stressful. Fortunately, the good news is, with some proper precautions, extra cleaning and sterilization you’ll be able to eradicate the bacteria. Knowing why baby formula bottles turn pink is only the first step in fixing the problem!

And what about when your baby bottle or nipple turn yellow? Read my article to find out what to do about it.

Photo of author


I’m Balint, founder of this site and a father (and dad) to a baby-turned toddler. I found the world of babies so fascinating that I started a blog dedicated only to that topic. By the way, I studied physics, engineering (PhD, MSc), and therefore I do a thorough research when I write about something. Since it’s a blog, of course I also write about my personal experiences.

Leave a Comment