Breast milk in the bathwater.

Desiree Bobby
Jan 7
5 min read

You see it pop up more and more often on social media: the advice to put old breast milk in the baby bath. The idea behind it sounds sweet and logical: breast milk is precious, natural, and gentle on the skin, so why not use it in the bath instead of throwing it away? But is this really so good? Or perhaps even harmful?

The idea of a milk bath sounds wonderful: a little of your own breast milk, warm water, a relaxed baby, and hopefully, calmer skin. And because breast milk is packed with protective substances, it seems logical that it can help the skin.

But as soon as you pour breast milk into a bath, something important changes: the concentration.

Breast milk is greatly diluted in the bath

The few small studies that do exist show that fresh breast milk can help with diaper rash in some cases, much like a mild ointment. These studies always involve applying breast milk directly to the skin, in a higher concentration, several times a day, and not rinsing it off.

A baby bath usually contains 3 to 8 liters of water. Many parents add a few milliliters to a maximum of 50–100 ml of breast milk.

That means:

The active ingredients in the milk are diluted thousands of times.

The protective substances in breast milk such as:

IgA antibodies
lactoferrin
lysozyme
growth factors

work in research especially when applied directly and in sufficient quantities to the skin or mucous membranes.

In a bath they are so spread out that only a tiny amount remains per skin surface, probably too little to have any real effect.

It's a bit like putting a drop of oil in a swimming pool and expecting your skin to get greasy.

Technically the oil is there, but not in an effective concentration.

The contact time is very short

A baby usually only spends 5 to 10 minutes in the bath . Afterward, you dry their skin, and most of what was on them is removed. As a result, very little of the active ingredients likely remain on the skin.

Many skin treatments, even something as simple as baby oil, work precisely because they stay on the skin and support the skin barrier for a longer period of time. This isn't the case with a milk bath.

Breast milk works differently when you eat it than when it's on your skin

Many of the benefits of breast milk operate primarily from within . In the gastrointestinal tract and immune system, the antibodies in breast milk are actively used, protected from breakdown, and absorbed precisely where they are needed.

This is much less effective on the skin. The skin is designed as a protective layer and doesn't let nearly everything through.

In addition, many substances in breast milk are:

proteins → sensitive to heat
unstable outside the body
not designed to penetrate through the skin

In addition, warm bathwater (often 37–38°C) can partially reduce the activity of some proteins. What works very powerfully internally can be much less effective externally.

And yet, adding a little milk can make the moment feel just that little bit more special.

This may all sound sober and “de-magic”, but there is also a soft side:

A fresh milk bath can contribute to:

moment of rest for you and your baby
warm skin-to-skin contact afterwards
relaxing ritual
caring attention

And it is precisely this stress reduction, safety and relaxation that indirectly support the skin and health.

Bath time may be even more about closeness and bonding than skincare, and a little fresh breast milk can be a small, loving extra.

And now the other side: old or spoiled breast milk

Because breast milk feels so precious, it's understandable that you want to conserve it. You've pumped for it, invested time and energy, and it's a shame if there are any leftovers. That's why you sometimes see the advice to use old breast milk you're no longer going to feed in the baby bath. But we need to be clear about this.

Spoiled breast milk is not safe, even in a bath.

Let's be clear: what do we mean by “spoiled breast milk”?

We speak of spoiled breast milk when, for example:

the milk has been stored for too long
he has been reheated several times
the milk has been too warm
it smells sour, rancid, or soapy
or when bacteria have been able to multiply

Furthermore, the longer milk is stored or the less favorable the temperature, the more its protective substances break down . The milk is then no longer soft and protective, but can actually cause irritation.

Why is spoiled milk not suitable for a baby bath?

There are a few important reasons and they mainly have to do with safety.

Spoiled breast milk can significantly increase bacterial growth. As soon as that milk enters the bath, it comes into direct contact with delicate baby skin, small cracks or wounds, and the mucous membranes around the bottom and genitals. This can lead to skin irritation and, in some cases, even infections, such as ear infections, especially in babies who are particularly vulnerable due to eczema, prematurity, or weakened immune systems.

In addition, these bacteria can ascend to the bladder via the urethra.

This risk isn't enormous, but it is real. This is especially true for girls, who have shorter urethras. Because a bladder infection in babies is often difficult to recognize and sometimes only causes vague symptoms, it can easily be overlooked. Therefore, the potential benefits of a bath with old or spoiled breast milk don't outweigh the health risks.

In addition, spoiled milk contains acidified fats and lactic acid bacteria. These can cause a stinging or burning sensation, redness, itching, or aggravate existing eczema. Not exactly what you want on delicate baby skin.

So there's one simple, safe rule you can remember:

If you are not going to let your baby drink the milk anymore, do not use it in the bath either.

And now you might be wondering: “But what do I do with those little bits of milk that are sometimes left over after a feeding or pumping?”

If you are going to give your baby a bath immediately afterwards and there is still a little bit of fresh breast milk left (for example, milk that has already been warmed up and that you would otherwise throw away), you can safely add it to the bath water.

It's fresh, clean and ready to use, and it can be a nice way for you to still make use of it.

In all other situations, I'd rather store that milk safely for drinking . That's where your baby truly benefits most. In the womb, breast milk can make a powerful contribution to your baby's health, immune system, and development.

Ultimately, that's where breast milk makes the biggest difference.

Love,

Bobby