"Soap" covers a lot of products that are chemically pretty different. Here's what's actually on the shelf.

True soap

Oils or fats reacted with lye. It's what handmade soap is, and what soap was for most of history. It's alkaline (pH around 9 to 10), cleans well and rinses easily, but can feel drying on sensitive skin and isn't good for hair. Olive oil soap and most artisan bars are true soap.

Syndet bars ("beauty bars")

Many supermarket bars aren't soap at all. They're synthetic detergent bars made with milder cleansers, closer to skin's pH. They're often labeled "beauty bar" or "cleansing bar" for exactly that reason. They're gentler for dry or sensitive skin.

Castile soap

Originally soap made only from olive oil, from the Castile region of Spain. Now it often means any all-plant-oil soap, usually liquid. It's very versatile, but it's still true soap, so it's alkaline.

Glycerin soap

The clear bars. Glycerin attracts moisture, so these feel less drying. Many are made with melt-and-pour bases.

Liquid hand soap

Usually a detergent-based cleanser in a pump, not true soap. It's the easiest option at a shared sink because there's no wet bar sitting in a dish.

Antibacterial soap

The FDA has said there isn't evidence that over-the-counter antibacterial soaps work better than plain soap and water for everyday handwashing, and it banned several antibacterial ingredients, including triclosan, from consumer hand washes in 2016. Plain soap and 20 seconds of scrubbing is the standard advice.

Which goes where

• Kitchen and bathroom sinks: liquid hand soap
• Shower, dry or sensitive skin: a syndet bar or a creamy body wash
• Shower, normal skin: any bar you like, true soap included
• Guest bathroom: small wrapped bars or a labeled dispenser, so each guest starts with something fresh

More on the handmade side in what is handmade soap.