Open pores are dilated openings of sebaceous or oil producing glands present on the face. These pores are bigger in size than the rest of the skin pores and that is why they are easily visible to the naked eye. Open pores can be shrunk in size to reduce their appearance with the help of a few treatments.
Open pores occur because of excessive oil production by these sebaceous glands during adolescence, leaving behind open pores as the skin matures. If you have oily skin, you are more likely to have open pores than someone who has normal or dry skin.