This is a Euphorbia, which is a succulent, not a cactus. The white latex-based sap it bleeds is pretty toxic and can cause blisters and rashes on skin and temporary blindness if it gets in your eyes. Be extremely careful when handling.

I don't grow this Euphorbia but it looks mostly healthy. The redness is probably just from sun exposure. Plants can tan just like we do :) (Plants should be acclimated slowly to sun exposure, though, to avoid burning.)

I would repot in a more gritty mix for better drainage. A 1:1 mix of cactus soil and perlite would work.

Edit: are the spots soft or mushy at all?

´Cactus soil´ is invariably mostly peat and is too moisture retentive for succulents generally. I use a well draining gritty mix, as do most growers here.

Hi Katie. This is Euphorbia trigona rubra. At least it looks like rubra to me. The only red I can discern appears to be normal coloration for rubra. Unless there is something else that I’m not seeing...?