Unneutered male cat keeps getting urine and melted litter on his testicles, only there

A male cat’s genitals may keep picking up urine and litter because of an incorrect urination posture or the litter itself. Usually both males and females squat to urinate; if a male sits, his genitals can contact urine and litter. Sticky litter can also cause it. Try a different litter to see if it helps.

Note that uncleaned urine and litter on the genitals can cause infection, so clean it promptly.