Valeric acid, or pentanoic acid, is a straight chain alkyl carboxylic acid with the chemical formula CH3(CH2)3COOH. Like other low molecular weight carboxylic acids, it has a very unpleasant odor. Valeric acid is commonly found in human feces, with an average concentration of 2.4 umol/g feces (range of 0.6-3.8 umol/g) (PMID:6740214). Valeric acid is produced by the gut microbiota, typically Clostridia species and other gut bacterial species such as Megasphaera massiliensis MRx0029 (PMID:30052654) via the condensation of ethanol with propionic acid (PMID:18116989). Valeric acid is largely considered as a gut microbial metabolite. Recently, valeric acid has been found to exert strong gut protective effects. Studies involving mice that received high doses of radiation showed that valeric acid replenishment (via oral gavage) elevated the survival rate of irradiated mice, protected hematogenic organs (such as the thymus and spleen), improved gastrointestinal (GI) tract function and enhanced intestinal epithelial integrity (PMID:31931652 ). Valeric acid was also found to restore the enteric bacteria taxonomic proportions and reprogram the small intestinal protein profile to normal levels. Valeric acid, like butyric acid, also appears to be a potent histone deacetylase (HDAC) inhibitor. High levels of HDAC proteins have been implicated in a variety of disease pathologies, from cancer and colitis to cardiovascular disease and neurodegeneration (PMID:30052654). Valeric acid is also found in certain plants, specifically in the perennial flowering plant valerian (Valeriana officinalis), from which it gets its name. Industrially valeric acid is primarily used is in the synthesis of its esters. Volatile esters of valeric acid tend to have pleasant odors and are used in perfumes and cosmetics. Ethyl valerate and pentyl valerate are used as food additives because of their fruity flavours. Hydrolysis of these valerate-containing food additives in the gut can also lead to the appearance of valerate in blood, urine and stool samples.