An ingrown hair happens when a removed hair (shaved, tweezed) curls back into the skin, causing inflammation, while a hair splinter (cutaneous hair embedding) is a sharp hair fragment (often from cut hair) that pierces the skin, migrating under it, common in barbers/hairdressers. Both cause painful, red bumps, but ingrowns stem from hair regrowth, often in curly-haired individuals, whereas splinters are foreign invaders needing removal to prevent infection, sometimes forming pilonidal sinuses, especially between fingers/toes. Ingrown hairs often to appear in areas of hair removal and growth, while hair splinters are often to be found on body parts that come into contact with loose, sharp, cut hairs. Always check your penis shaft and scrotum surface for these both.