quercetin concentration. A 2020 study demonstrated that quercitrin stimulated hair shaft growth in cultured human hair follicles. Volatile compounds responsible for pungency and tearing in onions when they are cut (e.g. syn-propanethial S-oxide gas). However, no formal studies have conducted to evaluate if these compounds promote hair growth or if they help other compounds to penetrate the skin to form hair follicles. To use the volatile compounds: Onions must be extracted and applied topically quickly before the volatile compounds evaporates. The extract will cause tearing eyes, but it can be prevented with a shower cap, or a pair of swimming goggles. To discard the volatile compounds: The onion juice is extracted and stored for a short while to evaporate the volatile compounds. The extract will not cause tearing eyes. Also, both genetically modified, and plant breed onions have been produced with significantly reduced levels of tear-inducing lachrymatory factor. Dietary supplements Dietary supplements are not typically recommended. Many people use unproven treatments, but there is little evidence of the effectiveness of vitamins, minerals, or other dietary supplements regrowing hair or retaining hair. There is no evidence for biotin (vitamin B7). While lacking both evidence and expert recommendation, there is a large market for hair growth supplements, especially for products that contain biotin. However, one small trial of saw palmetto which shows tentative benefit in those with mild to moderate androgenetic alopecia. There was no good evidence for gingko, aloe vera, ginseng, bergamot, or hibiscus as of 2011. Radiation-induced hair loss Radiation induces hair loss through damage to hair follicle stem cell progenitors and alteration of keratin expression. Radiation therapy has been associated with increased mucin production in hair follicles. Studies have suggested electromagnetic radiation as a therapeutic growth stimulant in alopecia. Cosmeses Certain hair shampoos and ointments visually thicken existing hair, without affecting the growth cycle. There have also been developments in the fashion industry with wig design. The fashion accessory has also been shown to be a source of psychological support for women undergoing chemotherapy, with cancer survivors in one study describing their wig as a "constant companion". Other studies in women have demonstrated a more mixed psychosocial impact of hairpiece use. Specialized tattoos, commonly known as scalp micropigmentation, can mimic the appearance of a short buzzed haircut. Human hair growth Type 1 and 2 5α reductase enzymes are present at pilosebaceous units in papillae of individual hair follicles. They