Why Soap Dissolves and 7.5 Ways to Make Your Soap Last Longer

You went to a farmer’s market recently and bought a pretty bar of goat’s milk soap. You love the soap but notice it doesn’t last as long as the Dove bars you used to buy. What’s going on? And is there any way to make your soap last longer?

First, a quick chemistry refresher (yay—and a shoutout to Dr. Collins, my Elvis-loving chemistry teacher in college). Soap is technically defined as “an alkali salt of fatty acids”. But…what does that even mean?? Depending on how long ago you took chemistry (and if you had Dr. Collins), you might recall that a salt is simply a reaction between an acid and a base. There are lots of different kinds of salts—table salt obviously, but also soap. Yup. Soap is created through a process called saponification: a chemical reaction between a weak acid (oil and/or fats) and a strong base (sodium hydroxide or potassium hydroxide). During saponification, the base splits the fat or oil into two components: fatty acids and glycerin. The fatty acids then attach to the sodium or potassium to create an alkali salt of a fatty acid (aka—soap) and glycerin.

Soap is a surfactant, which means it can bind to both oil and water. It is this ability that makes it an effective cleaning agent: one part of the soap molecule attaches to oil and grime, while the other attaches to water and allows it to wash away. Pretty neat. But what does this have to do with how long soap lasts? The answer lies primarily in the second half of the equation—the glycerin. Glycerin is a humectant; this means it attracts water. Humectants are good for your skin because they hold in moisture. The not-so-good-part? They hold in moisture. And excess moisture makes soap dissolve more quickly. Commercial soaps extract glycerin from the soap making process; while that will help them last longer, they lose the benefit of the glycerin. Handcrafted soap still has glycerin but as a result it won’t last as long. (There’s always a catch, right?)

 So…what can you do? Here are seven ways to make your soap last longer (plus an extra for good measure.)

1. Cut your bars in half. Use one half and store the other half in a cool dry place. I’m partial to my dresser drawer. Not only will your soap scent your clothes nicely, but it will continue to cure (evaporate any excess water) and only half your bar will be exposed to the damp environment of your bathroom. 

2. Make sure your bathroom is well ventilated. Open the shower curtain or door (when not in use, obv), use the exhaust fan, and open the bathroom door. Humid bathrooms hinder your soap from drying completely between uses.

3. Use cooler water. Easier said than done, especially in the winter, but it's true: hot water dissolves soap faster.

4. Alternate between two different bars. Use one bar for a week then set it aside to dry and use another bar for a week.

5. Use a well-draining soap dish. Yes, I make them and they’re quite lovely and unique if I say so myself but, any quality soap dish will work. You can support another fellow maker and find some interesting ones on Etsy or get a basic one on Amazon. Just don’t let them sit in a puddle of water.

5.5. Get a Soap Standle. Many years ago I was at a soap conference (yes, that’s a thing) and the creator of the Soap Standle came to pitch a gadget he had invented. It's similar to a soap dish, but not quite the same. It’s a small plastic tool that you stick on the bottom of a bar of soap which raises it up so the soap can drain and also creates a handle for holding the bar. You can use it with or without a soap dish. They really work!

6. Use a washcloth. A washcloth or bath pouf uses less soap than rubbing the bar over your body because it retains the later produced by the soap. Just be sure to hang these to dry afterward and clean/disinfect them regularly. A cotton washcloth can be put in the laundry. Bath poufs should be rinsed and shaken dry after every use. They should be soaked every 2-3 weeks for 5 minutes in a dilute bleach solution (3/4 cup bleach to 1 gallon water) and replaced regularly.

7. Use a soap bag. There are a few different versions of these; some are made with nylon mesh and others with cotton, hemp, or sisal. Place your soap inside the pouch and use it as an alternative to a washcloth. The surface of the bag lathers the soap quickly; afterward, hang it from the drawstring loop so the soap can dry. Like a bath pouf or washcloth, these should be cleaned and replaced regularly. Soap bags are also great for collecting and using all the little bits at the end of a bar.