28+ My Cactus Has Brown Spots. Brown spots on cacti can be caused by a wide range of problems, but environmental issues are usually the culprit. If you try to remove them, they are like a hard skin that comes off, the surface it's not a bug infestation because those are a brighter white color and fuzzy.
On the other hand if you are very attentive you will have a a fine specimen growing happily and that said, almost all cacti will be somewhat accepting of a shadier spot for a time, but.
If the cactus seems shrunken, wrinkled, or if the cactus is turning yellow or brown, it is getting too much sunlight and you should move it into a spot with better shade. For plants most closely associated with blazing sun and scorching sands, cactuses tolerate a surprising range of temperatures. When a cactus starts to turn brown and mushy at the top, it likely has something called tip rot (aka cactus stem rot). If your cactus is becoming wobbly, there's a good sign it has root rot—and the case may be severe if its base is brown or yellow.