What Causes Numbness On Penis?

Hello sir , I m komal. My question is about my husband. He is 25 yrs old. His some part of penis is numb. It wasn t like this,it started coming on last 2 weeks. His penis is of pinkish colour,but where the numbness has been started there is a slight discolouration. It doesn t look like incredibly strange,but like I said, where the discolouration is there is numbness.The parts where he still has sensation are remain pink. Also, he is loosing feeling about sex due to this. He is a healthy person and eats well. He doesn t smoke or drink or any wrong habit. He is shy to talk about this problem. But we are vry worried about this. is this lead to a big problem?Please give us advice to cure this problem as soon as possible. Thanks for reading this....