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The FD&C Act's cosmetic definition at sec. 201(i) expressly excludes soap. FDA's regulations narrow that further: a product is exempt as "soap" only if its non-volatile matter consists principally of an alkali salt of fatty acids, its detergent properties are due to those alkali-fatty acid compounds, and it is labelled and sold only as soap.

The consequences are neat and counterintuitive:

Product	Status
True soap, sold as soap	Not a cosmetic — regulated by the Consumer Product Safety Commission
True soap making a moisturising, deodorant or beautifying claim	A cosmetic
A syndet bar — synthetic detergents — however it is labelled	A cosmetic
Any bar with an antibacterial claim	An OTC drug

So the ingredient declaration requirement under 21 CFR 701.3 does not apply to true soap sold as soap, and a great many artisanal bars carry a full list voluntarily.

True soap is made by saponification — a fat or oil reacted with an alkali, sodium hydroxide for bars or potassium hydroxide for liquid soap. It produces fatty acid salts plus glycerin. Look for sodium olivate, sodium palmate, sodium cocoate, sodium tallowate on a list: those are saponified oils.

Two things follow from the chemistry:

• Soap cannot exist below about pH 9. It is alkaline by necessity, and that is why soap leaves skin feeling "squeaky" — it has raised surface pH and swollen the outer protein layer. Skin returns to its normal pH 4.5–5.5 over an hour or two, and does so more slowly with age and on damaged skin.
• Soap scum is calcium and magnesium salts formed with hard water, which is why soap leaves a film on skin, tiles and hair.

Syndet bars — Dove and its many imitators — use synthetic surfactants such as sodium cocoyl isethionate, and can be built at skin pH. They clean more gently and leave less scum, and they are legally cosmetics.

• Dry, eczematous or mature skin: a syndet bar, or a superfatted soap with a high free-oil content.
• Very oily skin, hands, general household: true soap is fine and cheap.
• Antibacterial claims are worth avoiding for domestic use. FDA's 2016 rule found that manufacturers had not demonstrated that consumer antiseptic wash ingredients — triclosan among them — were safe for long-term daily use or more effective than plain soap and water, and banned nineteen such ingredients from consumer antiseptic washes. Plain soap and water is the recommendation.
• Handmade soap is real soap, often superfatted and glycerin-rich, and it is exempt from ingredient labelling — which makes a maker who lists ingredients anyway worth preferring.

Not a cosmetic where the soap exemption applies — FDA files the rest under primary categories (12) personal cleanliness and (02) bath preparations. Antibacterial bars are OTC drugs under the antiseptic monograph.

In the EU there is no soap exclusion: soap is a cosmetic under Regulation (EC) No 1223/2009 like anything else, with full ingredient labelling, CPNP notification and a safety assessment. That is a genuine transatlantic divergence.

Two to three years, and a well-dried bar effectively does not spoil — the pH is hostile to microbes.

What matters is drainage. A bar left in standing water goes soft, slimy and wasteful, and the slime is partly dissolved soap and partly what has grown in it. Use a draining dish, and let bars dry between uses. Natural bars with high unsaturated oil content can develop orange "dreaded orange spots" — rancidity — and should be discarded.

• Bath and Body — the shelf this sits on, and the rest of it.
• Cosmetics — what the label is legally allowed to say, and the full catalogue.
• The rest of Washing — Body Wash · Shower Gel · Shower Oil · Hand Soap.
• Facial Cleanser — the same surfactant chemistry, gentler brief.
• Regulatory statements here follow the FDA and EU sources listed on Cosmetics, read 16 August 2026.