Hii , Welcome To HCM & Thanks For Asking Your Query Here I have gone through Your query and will try to provide information you need on it as you said you have noticed that your left testicle is about 10 % larger than right one for your information One testicle is often slightly larger than the other. This is usually normal and nothing to worry about. The left testicle usually hangs lower than the right one However, an enlarged testicle can be caused by variety of medical conditions including Hydrocele ,Epididymitis ,Inguinal Hernia , Mumps etc but seriously it needs thorough medical check up and investigation to make a confirm diagnosis you should not be worried as in your case nothing looks serious but still as you said you are feeling that testicle is less sensitive , i would strongly suggest you to have a visit to your Doctor to get it checked as soon as possible because any disease if diagnosed early than it is always easy to treat I hope it help Thanks & Get well Soon