How to make soap with milk, including breast milk

In this article, I will explain the process of making soap with any Milk and give tips to help you avoid the most common mistakes. Making soap with milk can be fiddley, but the results are worth it. Once you have tried it, then it doesn't seem so complicated.

Milk contains fats and proteins, which act as natural emulsifiers. This means you can get a lovely creamy bar of soap that is not as harsh on the skin.

White Soap with Jute string

Why is making soap with milk different from a standard Cold Process (CP) soap recipe?

You need to be careful when adding Lye to Milk because Milk has natural sugars, and if you heat it, you can caramelise or burn it. So if you didn't take some simple extra steps, you end up with yellow or brown spots or colour the whole soap a dark brown instead of a nice creamy white bar of breast milk soap. If this happens to you – you will know about it because it will continue to smell bad after a week.

When making soap with water, you must use a high percentage of lye water to create a reaction that results in saponification. Saponification describes the chemical reaction of lye water mixed with Fats, Oils, and Butters.

Lye is hot! When you pour your lye crystals into the water, it shoots up to over 80C (170F). If you look online, there are enough photos of injured soap makers from not taking the proper precautions. So always wear the right clothes and keep your skin, eyes and mouth covered, don't spill any, ever. If you are clumsy (like I am), ensure you don't walk around with the solution once you have mixed it. I do this in my workshop and open every door and window possible.

Many people add lye crystals directly to frozen milk blocks, which can work well too. You have to experiment and find what works best for you. I outline the different methods below; they all have positives and negatives.

Why is milk an excellent replacement for water in soap?

Raw milk contains antioxidants, vitamins A, D, B6, and B12, including biotin, calcium, protein, fats, and sugars. Saponification can alter the number of nutrients in your soap, but some remain.

The main reason people use milk in soap is that it lowers the pH level of your soap, which means it is gentler on the skin. So people who find soap typically too harsh and drying (because of the higher pH) will be more likely to enjoy a milk soap.

The lactic acids in your milk soap also makes the whole feeling on your skin just a little more luxurious and moisturising.

What kinds of milk can I use for making soap?

Any milk!

  • Human Breast Milk
  • Goats Milk
  • Horse Milk
  • Cow Milk
  • Donkey Milk
  • Sheep's Milk
  • Coconut Milk (okay, it isn't mammal milk, but it's still a thing)

It is worth noting that they all have different fat and sugar levels. For example, Goats Milk will add extra fat to your recipe, and Human Breast Milk has much less protein than Cow Milk and much more sugar. So depending on the milk, you might have to experiment a little.

Suppose you are using SoapCalc, don't add milk to the recipe (unless it is bovine milk, as it has an option for that). The simplest way to use the soap calculator when making milk soap is to keep the superfat % at no more than 5%.

Can I use sweetened condensed Milk instead of regular Milk?

No, you cannot use sweetened condensed milk to replace milk or water. It has something like 30 times more sugar than regular milk, so it would be more likely to burn. But having said that, it doesn't mean you can't add it.

It would be better to treat it like honey and stir it when your mixture is almost at trace, perhaps at the same time as any fragrance or other additive.

How do I add Lye to Milk without burning it?

There are five popular methods outlined below. And it is about finding the right one that works for you. The whole point of being careful with adding the lye crystals is to make sure you don't burn the milk, which smells horrible if you do. Making milk soap doesn't smell great for about a week after you have cut it; that is normal.

If you burn it, it will always smell bad, and all your excitement for your beautiful new soap will have to go into the bin. But never fear! If you have made soap before, you can do this too. You have to take care and take it slow.

Adding Milk & Lye: Method 1

Combine the water and milk without the lye crystals in a large container. Place the container in the freezer for 1 to 2 hours. It should get slushy, but don't let it freeze solid.

Then with safety gear on in a well-ventilated place, add 1/4 of the crystals to the cold milk water, and stir slowly. Wait 20 minutes and add another 1/4, and so on.

Take your time. Don't rush. We are trying not to burn the milk.

Adding Milk & Lye: Method 2

This is the 3:1 ratio. For example, perhaps your recipe calls for 400g of lye water, but you will replace 1/4 of that with your chosen milk, so 100g.

Mix the lye crystals (for your 400g water requirement) with 300 grams of water, and add this to the oils. Once the soap reaches a thin trace, add the milk and continue blending until a medium trace is achieved. Finally, add the remaining ingredients. Coming to Trace might happen faster than expected, so be prepared.

Some recipes suggest 50/50, but a point to note, the less water you have in your recipe, the faster it comes to trace, and if you are starting, it might be a little stressful! The recipe below has honey, which can also accelerate your trace.

Adding Milk & Lye: Method 3

Pour your milk (as a total replacement of the required water) into an icecube tray. Once the milk has completely frozen, take it out and put it into your Lye mixing container. Slowly, very slowly, add some of the crystals and stir continuously. Keep adding some more crystals until completely dissolved, and you will notice there is no more ice, and the milk is once again a liquid.

The temperature will rise as the lye flakes dissolve into the milk, so keep your eye on it. Another way to keep the temperature low is to put the container in another cold water tray, like an ice bath, as you continue to stir.

Make sure that the Lye dissolves completely, and you will know that this happens when the temperature stops rising, so keep an eye on your temperature. Either with a thermometer or a temperature gun. As mentioned before, if the milk gets too hot, it will discolour, and you will end up with smelly brown mush.

As an extra precaution, you can put your Lye milk solution through a sieve as you pour it into the oil mixture to ensure that everything dissolves.

Adding Milk to Lye: Method 4

Using the 3:1 water to Milk ratio (Method 2), mix your water and milk and then pour into icecube trays in the freezer overnight. Then slowly add your Lye crystals (Method 3).

The benefit of higher water content, so it will be slower to come to trace,

Adding Milk to Lye: Method 5

Method 5 is possibly the easiest of all and closely resembles Method 2. After you have mixed your lye water and oils and reached a light trace, continue to ensure the temperature is low. Add 1 or 2 ounces of milk along with your other additives, clay or essential oil.

It probably won't have the same creamy result, but it will still be a milk soap!

Gel Phase

Typically with Cold Process soap, you would insulate it overnight in a box, blanket, or warm oven. But because of the milk, you might consider putting it in the refrigerator instead and ensuring that rising temperatures don't scorch the milk. If you live in a hot environment, perhaps you want to put it in the freezer.

Putting your CP soap in the refrigerator or freezer prevents the Gel Phase. Some people love it. Some don't.

Smell Warning: because of the milk, it will not smell very nice for the first seven days. If it continues to smell after this date, you might have scorched your milk, and you can't use it as it won't ever smell lovely. However, I have made beautiful milk soap without any smell whatsoever.

Milk Soap Curing on rack
CP Refrigerated Milk Soap Cut and Curing,
scented with Frankincense and Lemon


After a few days, do a PET test. These little strips of paper will test the pH level of your soap. The easiest way to do this is to pick an end piece of soap you don't mind messing up and wet it a little. Then dip your PET strip of paper into it. You want to aim for between a 7-10 result. Anything above ten would be too harsh on the skin, with too much Lye, and you can't use it.

Some people do a “zap test”, where you use your tongue on the soap, and if it is zappy, like a zing off a battery, then it's too Lye heavy. I did this once… don't do it. It isn't enjoyable to have soap in your mouth! The paper is more accurate, and you don't have to wash your mouth with soap, haha!

I hope you enjoy making soap with milk.

Soap-making with milk is rewarding as it feels so luxurious on the skin and can also be moisturising and suitable for sensitive skin. It's also a great way to add nutrients, vitamins, and minerals to the finished product. For new moms, this method is excellent for using excess breast milk, too, especially if you spend a lot of energy expressing it.

Enjoy, and please let me know if you have any questions or how your recipe worked in the comments below. Remember, always use a lye calculator and wear safety gear.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.