A shaving soap is generally a hard block of soap that you use to whip up a lather with a brush. This lather then coats the face, protecting and lubricating the face and the razor. Few people still use shaving soap, opting instead for gel or foam. However, straight razor users and traditionalists still love using it.
Shaving soap is believed to have been developed at the start of the 19th century. Towards the middle of the 19th century, shaving sticks were developed (more on that later). Usually, shaving soap is sold with a flat bottom for those who use mugs, or with a shaving scuttle for those who apply straight to the face.
Shaving soap is seen as superior to creams and foams because it hydrates better. The soap removes all the natural oils from the hairs, which means that water can get into it easier, making it easier to cut the hairs. Another benefit is that, unlike cans of shaving cream or foam, shaving soap is approved by the TSA (Transportation Security Administration) so that you can carry it in your luggage.
The ingredients in shaving soap vary depending on the manufacturer. However, most soaps include either sodium hydroxide or potassium hydroxide. Tallow was also popular in the past and can still be found available. For a while, palm oil was used instead, but this is now highly controversial. Hence, coconut oil is more commonly available. The majority of shave soaps are now also paraben free.