Though flowstones are among the largest of speleothems, they can still be damaged by a single touch. The oil from human fingers causes the flowing water to avoid the area, which then dries out. Flowstones are also good identifiers of periods of past droughts, since they need some form of water to develop; the lack of that water for long periods of time can leave traces in the rock record via the absence or presence of flowstones, and their detailed structure.