Editing Stimulus modality (section)

===Odors===
An olfactory sensation is called an [[odor]].  For a molecule to trigger [[olfactory receptor neuron]]s, it must have specific properties.  The molecule must be:
# volatile (able to float through the air)
# small (less than 5.8 x 10-22&nbsp;grams)
# [[hydrophobic]] (repellant to water)

However, humans do not detect or process the smell of various common molecules such as [[nitrogen]] or [[water vapor]].

Olfactory ability can vary due to different conditions.  For example, olfactory detection thresholds can change due to molecules with differing lengths of carbon chains.  A molecule with a longer carbon chain is easier to detect, and has a lower detection threshold.  Additionally, women generally have lower olfactory thresholds than men, and this effect is magnified during a woman's [[ovulatory period]].<ref name="Wolfe" /> People can sometimes experience a hallucination of smell, as in the case of [[phantosmia]].