Odour can be very characteristic, but there is great variation in the ability to detect odour, and in the names given to odours. Odours of fungi are usually characterised by comparison to those of other things, such as vegetables; but sometimes specific odours can be recognised, such as that of phenol (a compound present in some species of Agaricus).

Crush a piece of the pileus to intensify the odour, which may also be stronger when the fruit-body is warmed (such as after being carried in a container in your pocket).

Human scent receptors are rapidly saturated, and odour can seem to disappear (the ability to smell the odour will come back after a while). Some odours are difficult to characterise, but the range of options provided here covers most odours that will be encountered among agarics. Some odours are pleasant when faint, but unpleasant when strong, and some of the categories grade into one another (choose more than one option if unsure).

Choose this state if: the odour is sour, rancid or unpleasant. The odour may resemble rotting flesh, faeces, fish, rancid flour or cheese (and even some fresh cheeses!), or is musty or generally nauseating.

An example of an unpleasant odour is the overpowering smell of Little Stinker (Marasmiellus affixus) which resembles a urinal that has not been cleaned for some time.

See also rubber or burnt hair, which is a quite specific unpleasant odour provided as a separate option. The term 'acidulous' (like acid) is taken to mean sour, rather than smelling of a particular acid. If a specific chemical (such as ammonia, chlorine or phenol) can be detected, choose chemical.