Why Does My Soap Smell Like Ammonia?

You unmold your beautiful goat milk soap, lean in for a sniff, and get... ammonia. Sharp, a bit like cleaning spray. Not what you were going for.

If you made milk soap, this is common, and in most cases it fades as the soap cures. Here's what's going on.

Why milk soap can smell like ammonia

When sodium hydroxide (lye) meets milk, it reacts with more than just the fats. Milk contains proteins, and when strong alkali breaks down proteins, it can release ammonia. Milk also contains sugars, which can scorch in the heat of the reaction, adding a burnt or "off" smell and a tan or orange color.

The ammonia smell tends to be strongest:

• Right after mixing lye into milk
• During the first days after unmolding
• In soaps with lots of milk
• When the batch got hot

Does the ammonia smell go away?

Usually, yes. Most soap makers find the smell fades during the normal cure time (commonly around 4-6 weeks) as the soap dries and finishes saponifying. Let bars cure somewhere with good airflow, spaced apart, out of direct sun.

If the smell is still strong after a full cure, see the other causes below.

How to prevent it next time

1. Freeze the milk.
Freezing milk into cubes or slush before adding lye keeps temperatures down, which reduces scorching and smell. Add lye slowly while stirring.

2. Add lye slowly and keep it cool.
Work in stages, and set your container in an ice bath if needed.

3. Try the split method.
Some makers dissolve lye in part of the water, then add milk at trace or blend it into the oils instead of mixing lye directly into all the milk.

4. Soap cooler.
Avoid heating the batch. Some milk soap makers skip insulating molds, or pop freshly poured milk soap into the fridge or freezer for a day to prevent overheating (gel phase), which can reduce browning and smell.

5. Use less milk.
Replace part of the liquid with water if the smell bothers you.

Other reasons soap can smell off

• Rancid oils (dreaded orange spots, old oils): smells stale, crayon-like or like old cooking oil, not ammonia
• Fragrance issues: some fragrance oils morph or react with lye
• Contamination: unclean equipment, spoiled milk

Safety notes

• Always follow proper lye safety: goggles, gloves, ventilation
• Mix lye solutions in a well-ventilated area. The fumes, especially with milk, aren't pleasant
• Don't use soap before it's fully cured and tested

Store-bought soap that smells like ammonia?

That's unusual. It may be old, stored in heat or damp, or the product may have gone off. If a bar smells strongly of ammonia and it's causing irritation, stop using it.

FAQ

Why does my goat milk soap smell like ammonia?
Lye can break down milk proteins, releasing ammonia. It's common in milk soaps and usually fades during cure.

Will the ammonia smell go away in soap?
In most cases it fades over the curing period of several weeks.

How do I stop milk soap from smelling like ammonia?
Freeze the milk, add lye slowly, keep the batch cool, and consider using less milk.

Is soap that smells like ammonia safe?
Properly made, fully cured milk soap with a fading ammonia smell is typically fine. Test and cure fully before use.