The number can vary depending on genetics and face size, but on average it's around 300,000.

The size of your pores can depend on many factors, including your skin tone and type. Lighter skin tones and drier skin types tend to have smaller pores. Darker skin tones and oilier skin types tend to have more noticeable pores.

The most common causes are aging and sun damage. Clogging from excess oil production and picking at skin or squeezing a pimple can also cause pores to become stretched over time. Another factor is dehydration–moisture-deprived cells flatten, increasing the gaps between cells, which can make pores appear larger.

The "dirt" is actually the colour oil turns when exposed to the air–it oxidixes, similar to the process of an apple slice turning brown. Bacteria multiply, feeding off the oil. Some skin pigment (melanin) ends up in the oil, so the darker the skin, the darker the oil.

Active oil glands under the surface mean large pores at the surface. As excess oil accumulates at the surface, it can combine with shedding skin cells to produce blackheads. Chronic blackheads may stretch pores and make them larger.

Recent studies show that pores grow both larger and longer, forming a more elliptical shape as we get older.

Daily skin care is essential to reducing pore size. Cleanse to remove excess oil and cellular debris that accumulates in pores, then follow with gentle exfoliation to remove any additional dead skin cells. Finally, apply a light moisturizer to plump and hydrate skin.