Ingrown Hairs Sources
According to the British Association of Dermatologists (2021), using a razor with a single blade reduces pseudofolliculitis (ingrown hairs and bumps).
This is corroborated by Dr Norwood (2016), who suggests:
"Multiple-blade razors that cut the hair at skin level or just below the skin’s surface should be avoided."
References:
1. British Association of Dermatologists (2021). Pseudofolliculitis. Patient information Leaflet.
2. Norwood, D. (2016). Pseudofolliculitis Barbae: Prevention and Treatment. US Pharm.