What is the difference between soap, shampoo, and detergent?

Answer 1

From Wikipedia:

Soap: Many soaps are mixtures of sodium (soda) or potassium (potash) salts of fatty acids which can be derived from oils or fats by reacting them with an alkali (such as sodium or potassium hydroxide) at 80°–100 °C in a process known as saponification. The fats are hydrolyzed by the base, yielding glycerol and crude soap. Historically, the alkali used was potassium made from the deliberate burning of vegetation such as bracken, or from wood ashes.

Originally soap and shampoo were very similar products. Shampoo formulations seek to maximize the following qualities: Easy rinsing / Good finish after washing hair / Minimal skin/eye irritation / No damage to hair / Low toxicity / Good biodegradability / slightly acidic pH, since a basic environment weakens the hair by breaking the disulfide bonds in hair keratin. Many shampoos are pearlescent. This effect is achieved by addition of tiny flakes of suitable materials, eg. glycol distearate (a wax). Surfactants, also known as wetting agents, lower the surface tension of a liquid, allowing easier spreading, and the interfacial tension between two liquids. The term surfactant is a contraction of "Surface active agent".

Detergent: especially those made for use with water, may include different components having some or all of the following properties: surfactant to 'cut' grease and to wet surfaces / abrasive to scour / substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to destroy dirt / water "softeners" are used to counteract the effect of "hardness" ions on other ingredients / oxidants (oxidizers) for bleaching and destruction of dirt /
materials other than surfactants to keep dirt in suspension / enzyme to digest proteins, fats, or carbohydrates in dirt or to modify fabric feel / ingredients, surfactant or otherwise, modifying the foaming properties of the cleaning surfactants, to either stabilize or counteract foam plus ingredients having other properties to go along with detergency, such as optical brighteners, softeners, etc., and colors, perfumes, etc. "

So, to answer your question -- while they are all, at heart, cleaners, the added ingredients make all the difference!!

Answer 2

Soap- for hands and body.
Shampoo- for hair.
Detergent- for clothes.