Comedogenicity is the scientific word that refers to the likelihood of an ingredient or substance to clog pores, and thus lead to an acne lesion. It will be good to see more studies on this subject, but of the dozen or so studies that researchers have produced thus far, we now know of some ingredients that might be pore-clogging, and others that are likely safe.
Oils: Not all oils are comedogenic. While some oils like coconut oil and sweet almond oil will most likely clog pores, other oils like jojoba oil, sunflower oil, and safflower oil will not.
Product labels: You will notice many products claiming "non-comedogenic" on the label. This claim is completely unregulated, so buyer beware. Take matters into your own hands and avoid comedogenic ingredients when they are listed in the top seven (7) ingredients on a product's ingredient list.