Handmade soap is made without synthetic preservatives or artificial hardeners. One of the great things about handmade soap is that it does not need these things added to them. If made and stored properly your handmade soap will be very hard and long lasting.
The number one rule for prolonging the life of your soap is to make sure it does not sit in a pool of water between uses. Get a good soap dish that allows the water to completely drain away from the soap. The best type of soap dish will also allow air to circulate around the bar. It is even better if you can let your soap completely dry between uses. For soap that is unused store it in a dark cool place like a lingerie drawer or linen closet.