hormesis (n.), hormetic (adj.)

https://doi.org/10.1351/goldbook.14745
Unexpected and unexplained but favorable biological response to low-level exposure to a substance or physical agent generally considered to be harmful.
Source:
PAC, 2009, 81, 829. (Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)) on page 897 [Terms] [Paper]