Well depending on the cannabis oil, it is often mixed with a carrier like coconut oil. If it has a label you may want to look at that to see. Otherwise, coconut oil is a common carrier. You can also mix it into a regular skin lotion or massage oil. There are some great brands out there like Sweet ReLeaf or Flower Power that are pre mixed. Hope this helps!
Cannabis comes in a variety of oils including tinctures (to be taken sublingual), oral capsules, creams, essential topical oils, and concentrated oils for vaporizers, etc. Consider which type of oil you have purchased before applying. Cannabis creams/salves are not mixed with anything, and are often applied liberally to an area of pain, where as topical essential oils are applied in smaller quantities as they often contain more concentrated psychoactive ingredients. If you purchased your "cannabis oil" without a medical marijuana card in California you most likely purchased "hemp oil." Hemp oil, unlike cannabis oil has only trace amounts of THC and CBD, and therefore will be 100 times less potent than cannabis oil.
I'm with Pamela on this one. The only topical I use are whole plant cannabis oil mixed with coconut oil as a carrier. The only downside is that you might have to heat the mixture as coconut oil does go solid when it's colder, but I run mine under hot water for a few seconds and it's ready to go. Plus coconut oil is all natural and great for the skin