Good Soap Takes Time
Have you heard the term "fresh soap"? This term makes my skin crawl a little. As a soap maker, I know that good soap takes time. Handmade soap can take weeks and even months, in some cases, to cure fully. Fresh soap, while it is still soap, has a higher ph which causes it to be harsher on the skin. It is also softer and will not last as long as a properly cured bar.
When we use soap to wash our skin, the ph is important because we don't want to strip our skin and leave it irritated and tight feeling. But if the ph level in our soap is too high, this is exactly what will happen.
Soap, of necessity, and by definition is alkaline. We use the chemical sodium hydroxide (for making a solid bar of soap) to rearrange the properties of chosen oils to give us our salt/water/glycerine product we know as soap.
When you mix butters and oils, which are also known as triglycerides, with sodium hydroxide they break down into their core components namely glycerine and fatty acids. Depending on your choice of butters and oils some will be short-chain fatty acids and some will be longer chain fatty acids
The fatty acids combine with the hydroxide portion of sodium hydroxide to create sodium salts also known as soap. But, the process is not complete at this stage. The sodium salts then need to further align themselves into complex structures called soap crystals.
While your soap batter is still liquid, short-chain fatty acids begin to form into salt crystals together with some of the longer chain fatty acids. Saponification is complete within around 48 hours, ie all the hydroxide has been turned into sodium salts, but during the continuing cure time, the longer chain fatty acids are still busy rearranging themselves into soap crystals and this is what helps your soap to become harder as time goes on. Not just the water evaporation which mostly occurs within the first 2 weeks.
If you use your soap before it has fully cured, it will dissolve more quickly. Not just because it has a higher water content but because not all of the longer chain fatty acids have formed soap crystals. It is the crystalline component of soap that is predominantly made up of longer chain fatty acids which give hardness and durability.
At a minimum, we cure our soaps for 4 weeks. However, most of them sit for 6+ weeks before they are ever listed. Don't fall for the "fresh soap" marketing. Good soap takes time to make sure you have a quality product.