Soap is almost the oldest way to clean the skin because it has been used for many thousand years. While water also clean the body, wash dirty oil from skin. However that's not enough for your skin. Therefore using soap should be better. But selecting appropriate soap can reduce side effect such as irritation, dry skin, rash, skin infection or chemical sensitive skin.
Soap has been produced from saponification process which is a chemical reaction between various oils and fats and caustic soda (lye or NaOH). It can be washed by water. There maybe fragrance or dye added for desirable scent or color. However natural soap will use only natural compound. Glycerin which is in natural soap will moistur the skin.While glycerin in commercial soap will be extracted for making moisturizer later. So this soap will dry skin and consumer need moisturizer.
– Hard Soap. White or gray-white bar when it's dry and cold. a soap made with olive oil, or some other suitable oil or fat, and sodium hydroxide
-Soft Soap. Like honey or jelly. Yellow. It's made of olive oil and soda
-Liquid Soap. It's made of Potassium Hydroxide. Sometimes hog plum oil, bean, cotton seed is added.
-Syndet. It's composite of moisturizer.
In addition, there are some kinds of soap with different ingredients depend on objective. For example, soap with triclosan and triclocarban is antibacterial soaps. Soap with lanolin moisturize skin. So selecting soap depends on skin type and objective.
Soap can irritate your skin. It makes skin dry or parched. In worse case, there are fracture on skin. However usually if you have normal skin, you will have no problem along you often use soap. So your skin will lose oil which covers your skin for chemical harm protection.