- Xanthoma
- A skin condition characterized by raised patches.
- Xenoparasite
- An organism not usually parasitic on a particular species, but becomes so when the immunity of the host becomes weakened.
- Xenopsylla
- A genus of flea that includes more than thirty species, many of which transmit disease-producing microorganisms, as is the case of the rat flea, X. cheo’pis, which transmits Pasteurella pestis, the causative organism of plague, and Rickettsia typhi, the causative agent of typhus.
- Xerostomia
- A diminished secretion of saliva, causing an abnormally dry mouth, often seen as a side effect from certain medications.
