The Evidence...

[1] - Mínguez-Alarcón L, Gaskins AJ, Chiu YH, Messerlian C, Williams PL, Ford JB, Souter I, Hauser R, Chavarro JE. Type of underwear worn and markers of testicular function among men attending a fertility center. Hum Reprod. 2018 Sep 1;33(9):1749-1756. doi: 10.1093/humrep/dey259. PMID: 30102388; PMCID: PMC6530653.

[2] - Mieusset R, Bujan L. The potential of mild testicular heating as a safe, effective and reversible contraceptive method for men. Int J Androl. 1994 Aug;17(4):186-91. doi: 10.1111/j.1365-2605.1994.tb01241.x. PMID: 7995654.

[3] - Parazzini F, Marchini M, Luchini L, Tozzi L, Mezzopane R, Fedele L. Tight underpants and trousers and risk of dyspermia. Int J Androl. 1995 Jun;18(3):137-40. doi: 10.1111/j.1365-2605.1995.tb00400.x. PMID: 7558376.