What's wrong with my Cactus?

Hi All,

I'm new to the forum and hope you can offer some help! I just moved in with my boyfriend and we put his cactus on top of our bookshelf in the living room. I've noticed it's developed some brown spots on it not just at the base but also the top and along the body. It looks like something is chewing away at it but I haven't been able to clearly identify what it may be? Is it just rot from over-watering? Or do you think there is a more serious issue? I love the little guy and want to make him healthy!

Thanks,

Mishuko

your picture is blured so i cant see exactly but i think not enough sun light is the main problem mishuko...if possible, try to place it near bright window, not on the top of your bookshelf...and stop watering it during the cold winter time! hope it helps.