Question: How to thin out a thick lotion?

Someone asks: Say you have a cream that came out too thick and you have to thin it. You measure out the water and just add? THEN how do you refigure the % of your original formula?

You cannot thin out a thick lotion once you've made it. If you add water to it, you'll mess up the emulsion and the preservative. Heating it up and adding more water will make our not-heat loving ingredients like preservatives, panthenol, silicones, and so on very upset and they may become de-activated or might give off a horrible smell or might mess up the skin feel. So if you've made a thick lotion and want it thinner, you'll have to make notes for next time that you wish to alter it.

Let's use my basic body butter recipe as our template here as it is a very thick creamy buttery lotion.


RECIPE FOR A BODY BUTTER
WATER PHASE
60% water
2% sodium lactate or glycerin

OIL PHASE
10% oils (4% light, 4% medium, 2% heavy, or just 10% of the oil of your choice)
15% shea butter (or butter of choice)
6% emulsifier
3% cetyl alcohol

COOL DOWN PHASE
0.5 to 1% preservative
1% fragrance or essential oil blend

So what's thickening this recipe? Two main ingredients - the butter and the cetyl alcohol. You can leave out the cetyl alcohol and increase the water amount by 3% and you could reduce or even eliminate the butter. (The emulsifier helps thicken as well - we can't remove it, but we can reduce it.)

Whenever you remove something from a lotion, add the different to your water amount. So if you choose to reduce your butter amount to 5%, add 10% to the water phase. You can use any water soluble ingredients you choose - aloe vera, hydrosols, a combination of things like panthenol or proteins, but you have to add the amount into the water phase to get 100%.

Plus you need to look at your emulsifier amount. If you are using Polawax, it's about 25% the oil phase. So if we remove the cetyl alcohol and reduce butter, we lose 13% of our oil phase, and it becomes a total of 15%. So 25% of that would be 3.75% emulsifier, but I'll round it up to 4. (If you're using other emulsifiers, you'll have to read the manufacturers' suggestions for usage rates.)

So let's take a look at our new recipe!


MODIFIED RECIPE FOR A BODY BUTTER
75.5% water
2% sodium lactate or glycerin
10% oils (4% light, 4% medium, 2% heavy, or just 10% of the oil of your choice)
5% shea butter (or butter of choice)
4% emulsifier
0.5 to 1% preservative
1% fragrance or essential oil blend

I've increased the water amount to compensate for the reduction in the other ingredients. This should make thinnish lotion.

Let's say you're modifying on the fly and decide to add 80 grams of water to this recipe as you're making it (or, as often happens to me, your hand slips). Total up what you used in the recipe and divide by the total amount to get your percentage. (For more detail on how to get the percentages in the lotion, check out this post.)

MODIFIED RECIPE FOR A BODY BUTTER
80 grams water
2 grams humectant
10 grams oils
5 grams shea butter
4 grams emulsifier
0.5 grams preservative
1 gram fragrance oil
Total 102.5

So divide each ingredient by 102.5 to get your percentage

80 grams water / 102.5 grams = 78.05 grams of water
2 grams humectant / 102.5 grams = 1.95 grams of humectant
and so on...

Or you can just live with it being 102.5% and recognize that if you make a 10 times batch of the stuff you'll get 1025 grams instead of 1000. (I do this for small amounts over 100%. If you're at 110%, you'll want to recalculate the recipe.)