Common facial products, such as beard oil, will contain a number of different ingredients. Among the ingredients you'll find carrier oils, of which there are a plethora, each with its own comedogenic rating.
Comedogenic is something which blocks pores, causing acne and blackheads to appear. The higher the rating of an oil, the higher chance it has of clogging pores. Generally, ratings go from 5 to 0, with zero having no chance of blocking pores.
Everyone is different, however, so an oil that works for one person may not work as pleasantly for another. This is in regards to whether the oil's comedogenic rating is 5, 1, or anything in between. With that in mind, using less product and allowing several weeks for your skin to adapt is a good way of getting rid of non-allergy imposed side effects.
Here's a small list of some of the most common skincare oils and their comedogenic ratings. Keep in mind that some in this list are indeed DHT Blockers, which you'll want to avoid applying to your facial hair area, should your goal be to attain more beard growth and coverage.
5 = High chance of clogging pores / 4 = Moderately high chance / 3 = Moderate chance / 2 = Moderately low chance / 1 = Low chance / 0 = Does not clog pores.
Also beeswax, which isn't an oil, has a comedogenic rating of 2. It's a popular ingredient found in mustache wax, to help give a strong hold. Shea butter, found in most beard balms, has a rating of 0.