TLDR Testosterone can slow down hair growth when combined with certain cells from bald scalps, and this effect can be blocked by an androgen receptor blocker.
In 1996, a study was conducted to understand the role of testosterone in hair growth inhibition using dermal papilla cells from the bald scalps of postpubertal stumptailed macaques. The study found that testosterone did not affect the proliferation of dermal papilla cells or outer root sheath cells when cultured separately. However, when co-cultured, testosterone inhibited the proliferation of outer root sheath cells, but only when the dermal papilla cells were from the bald scalps of adult macaques. This inhibition did not occur with dermal papilla cells from the hairy scalps of adult macaques or the pre-bald scalps of juvenile macaques. The study also discovered that RU 58841, an androgen receptor blocker, antagonized the testosterone-induced inhibition, suggesting that androgens may play a crucial role in hair growth and baldness. The study concluded that testosterone's inhibitory effect on epithelial cell proliferation is age-dependent and may involve the induction of repressors or growth factors from dermal papilla cells.
11 citations,
October 1994 in “The Journal of Clinical Endocrinology and Metabolism” Finasteride increases hair growth, prolongs hair cycle, and lowers dihydrotestosterone levels.
49 citations,
January 1994 in “The Journal of Steroid Biochemistry and Molecular Biology” RU 58841 may treat acne, hair loss, and excessive hair growth.
22 citations,
December 1991 in “PubMed” 
53 citations,
May 1986 in “Clinics in endocrinology and metabolism” Androgens like testosterone affect hair growth and oil production differently across body parts and individuals.
157 citations,
April 1994 in “Clinical endocrinology” Androgens can cause hair growth in some areas and hair loss on the scalp.
5 citations,
September 2021 in “Frontiers in Cell and Developmental Biology” Dihydrotestosterone treatment on 2D and 3D-cultured skin cells slows down hair growth by affecting certain genes and could be a potential target for hair loss treatment.
19 citations,
January 1997 in “Endocrinology” Testosterone can slow hair growth in adult monkeys, but a blocker called RU 58841 can counteract this and potentially help hair regrow.
1 citations,
May 2017 in “InTech eBooks” Hair loss in Androgenetic alopecia (AGA) is due to altered cell sensitivity to hormones, not increased hormone levels. Hair growth periods shorten over time, causing hair to become thinner and shorter. This is linked to miscommunication between cell pathways in hair follicles. There's also a change in gene expression related to blood vessels and cell growth in balding hair follicles. The exact molecular causes of AGA are still unclear.
1 citations,
March 2021 in “Skin health and disease” Better hair loss models needed for research.
