I have red spots that occasionally show up on my arms and sometimes are itchy they usually come and go. i'm wondering if they could be skin cancer?

Skin Rash: A skin rash that comes and goes is not skin cancer. Your rash could be one of many things, ranging from "neurodermatitis" to a reaction to drugs you are taking, irritants in your environment, or a whole host of other causes. It is best to consult a dermatologist if it continues to concern you.

Probably not: While possible, bumps that tend to come and go are generally not cancer. Skin cancer lesions tend to grow.

Unlikely : Skin cancer usually is a slow growing lesion which doesn't go away on it's own. Precancerous lesions such as actinic keratoses can go away if you use enough sun protection. Rashes also commonly can come and go. I recommend seeing a dermatologist when you have an active lesion for an evaluation and potential skin biopsy.