Baby Formula Smells Bad (like Fish, Dog Food, Poop, or Metallic)?

Balint Horvath, PhD

Writer, parent, and veteran of baby feeding battles.


Wondering why your precious baby formula smells so bad, reminding you of fish, dog food, poop, cheese, broccoli or just smells metallic? The first time I smelt infant formula I found it quite offensive! It certainly didn’t  smell like breast milk! Let’s explore what makes infant formula smell the way it does and when you should be worried.

Baby formula smells unpleasant because of the different ingredients used to make it. The main culprits are hydrolyzed proteins, amino acids, vitamins, and minerals. Hypoallergenic formulas smell worse than regular formulations. Spoiled formula smells worse and should be tossed. 

Key takeaways

  • Baby formula has a strong smell that ranges between smelling like cheese, fish, or metal. 
  • Ingredients such as DHA, vitamins and minerals, and hydrolyzed proteins are responsible for unpleasant odors.
  • Specially formulated formulas for sensitive stomachs can smell like dog food.
  • Hypoallergenic formulas smell extra strong because of the extensive hydrolyzed proteins.
  • Different formula brands use unique ingredients and formulation which changes the way the product smells. 
  • Bacterial growth and separation are signs of formula spoilage as well as a baby that vomits after a feed. 

How should baby formula smell?

Each brand has its unique formulation with some infant formulas smelling similar to cheese while others have a fishy or even metallic odor. This is because of the ingredients used to produce nutritional infant formula. 

As unpleasant as these smells may be, it’s pretty normal for baby formulas, especially those containing hydrolyzed proteins. If you read through the list of ingredients used to make up the formula, you’ll notice a huge amount of vitamins and minerals are included. These are also responsible for a distinct and often, foul smell. 

Why does baby formula smell like fish?

If your baby’s formula smells like fish, the main culprit is Docosahexaenoic acid, more commonly known as DHA. This is an important nutrient for the healthy development of your baby’s brain and eyes. DHA is an omega-3 fatty acid that’s found in certain fish and algae. 

It’s not unusual for your usual formula brand to sometimes smell fishier than normal. This is because some batches are made with stronger DHA although this doesn’t alter the required level as stipulated on the packaging label. 

Why does baby formula have a metallic smell?

For me as a father bottle-feeding, baby formula smells metallic because of the vitamins and minerals used to meet the essential nutritional requirements. Baby formula manufacturers use a range of minerals and vitamins to mimic breastmilk as closely as possible. 

However, the addition of these ingredients will alter the way your infant’s formula smells and tastes. 

Why does baby formula smell like dog food?

When baby formula smells like dog food, you can’t be faulted for thinking it’s gone bad! However, if you notice the same smell with every container you open, it’s probably linked to the ingredients used. Some parents report this smell with infant formulas specially formulated for sensitive tummies.

Why does baby formula smell like poop?

When baby formula smells like poop, you can start to get worried. Try and determine if the odor has changed significantly from the previous container or does it simply smell sour (and reminds you of a bad case of diarrhea.) Either way, if the smell rings alarm bells, rather throw the batch away or return it to the retailer. 

What causes baby formula to spoil?

The following factors can cause baby formula to spoil:

  • Feeding time after preparation: The formula can spoil two hours after it’s been prepared if not stored in the refrigerator. If you keep prepared formula in the fridge, make sure your baby drinks it within 24 hours.
  • Bacterial contamination: If you keep leftover formula from a feed it can spoil very quickly. The presence of your baby’s saliva in the formula can cause bacteria to grow and contaminate the contents of the bottle. Some recalled formulas are contaminated by bacteria while manufactured in a factory.
  • Incorrect or damaged sealing: Bacteria, dirt, and air can spoil liquid or powdered formula not properly sealed. 
  • Incorrect storage: Unopened formula should be stored in a cool, dry place to prevent spoilage. 
  • Expiry period: Opened infant formula should be used within one month of being opened otherwise you run the risk of it going bad. 

When asking whether used baby bottles are safe, consider factors such as bacterial contamination which can spoil the formula and be dangerous for your little one’s health. 

Specific formula smelling bad

Why does soy formula smell so bad?

A soy-based formula can taste quite different from other types of infant formulas with most parents complaining about its unappealing smell. The smell is often described as something similar to sour beans or old hay with some parents saying the formula smells like broccoli. 

While the odor may be unpleasant, it’s not bad but merely caused by the soybeans proteins used to make the infant formula.  

Why does hypoallergenic formula smell so bad?

If you’re switching your baby to a hypoallergenic formula, you’re likely to notice a stronger, different smell. This is because the milk proteins have been broken down into an extensive hydrolyzed formulation which is responsible for the strange smell. The milk proteins may become amino acids which cause the formula to smell stronger. 

Bobbie formula smelling fishy?

Bobbie formula often smells fishier than other brands and for a good enough reason. Bobbie Baby Organic Powder Formula is made with several ingredients including algae. The algae is responsible for the DHA component of the formula. 

Enfamil (Gentlease) smelling bad?

Most parents will tell you that Enfamil (Gentlease) smells no worse than any other brand. Tap water can alter the smell of prepared Gentlease. We found using filtered water reduces the strong odors when preparing bottles for our baby daughter. 

Nutramigen smelling bad?

Hypoallergenic baby formulas generally have an unpleasant aroma but Nutramigen’s special formulation takes the smell to another level! Nutramigen includes Enflora LGG and PurAmino, both ingredients responsible for the product smelling bad. This formula is made extensively with hydrolyzed casein protein to reduce an allergen response but it does produce a strong odor. 

Similac (Alimentum) smelling so bad?

It’s normal for Similac (Alimentum) to smell unpleasant because of the hydrolyzed protein used to reduce allergies in sensitive babies. The ready-to-feed product has a slightly less offensive smell compared to the powder formula but it’s not as cost-effective. 

Aptamil smelling bad?

Some parents complain that Aptamil formula smells like poop which is very off putting but it does have a pretty bad aroma. Some Aptamil products include soy and fish, both ingredients responsible for stronger-smelling infant formula. 

Best-smelling formula to consider

While most bottle-feeding parents will tell you that all infant formulas smell bad, some brands have a gentler aroma. Despite some parents complaining about Enfamil Gentlease smelling bad, others have found it to be one of the best-selling options on the market. 

Any formula that isn’t made with extensively hydrolyzed protein is going to smell better than those manufactured with this ingredient. 

How to tell if baby formula is spoiled?

Bacteria growing on the rim of tins 

If you see signs of bacteria or mold growing on the rim of the tin, toss the formula immediately. This is a sign that the infant formula has been contaminated and should be avoided at all costs. The growth of bacteria inside the tin will cause the lid of the container to swell and the rim or seal to break. 

The formula looks clumpy 

If the formula looks clumpy it may have been exposed to moisture and has become spoiled. This could be a result of poor or damaged sealing during packaging or storing an opened container in a damp environment. Clumpiness also happens when the ingredients start to break down and cause the formula to separate when mixing it with water. 

Your baby gets ill after drinking

If your baby starts to vomit or have diarrhea after a feed, the formula could be off. This often happens when a prepared bottle has been left at room temperature for more than two hours before feeding. Storing prepared formula in the fridge helps to prevent it from spoiling too quickly. 

Recalled baby formula has been spoiled – watch this video to find out more.


If your baby bottle smells of soap don’t be surprised if the formula ends up smelling off as well! It takes getting used to the strong and sometimes offensive smell of baby formula. But once you’re bottle-feeding like a pro, you’ll hardly notice the unpleasant aromas. Take it from me as a father who has been there and done it!

And if your baby bottle smells like old milk, here’s my article on how to get the milk smell out of such bottles.

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