The hardening of testicles may be related to low temperature, or it may be related to epididymitis-orchitis, testicular torsion, testicular tumor and other etiologies. 1. When the weather is cold or exposed to cool water, etc., due to thermal expansion and contraction, the testicles may become hard, usually not accompanied by other symptoms, this is a normal physiological phenomenon. 2. In epididymo-orchitis, the testicle may also become enlarged, painful and hard. 3. Testicular torsion can also cause pain, swelling and hardening of the affected testicle. 4. When you have a testicular tumor, there is usually a hardening and gradual increase in the size of the testicle. If the testicle becomes hard, you need to go to the hospital, complete the testicular ultrasound, testicular tumor markers and other related examinations, and identify the specific cause of the disease before giving appropriate treatment.