When oil glands churn out excess sebum (typically due to hormonal upsets), pores can&rsquo;t keep removing the bacteria breeding ground.&nbsp;
The Fix: &ldquo;Decreasing sebum production from the start prevents pores from becoming oversaturated with oil,&rdquo; says Dr. Brandt, who suggests products laced with antiseptic botanicals to curb oil and minimize the appearance of pores. But if breakouts are chronic, pull out the in-office big guns. Dr. Brandt recommends a series of Isolaz (aka photodynamic therapy) treatments &mdash; essentially a bacteria-blasting Dyson for pores. Sessions run about $200 each; four to eight weekly treatments are typically needed. 
The Product:&nbsp;<a target="_blank" href="http://bit.ly/1oH84zS">Dr. Brandt Pore Thing Pore Tightener</a> ($45) uses lentil seed, eijitsu rose and alpine lichen extract to zap oils.
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"Over time, collagen levels in skin naturally decrease," explains Dr. Brandt. "This causes skin, including pore walls, to become lax overall."
The Fix: Derms swear by vitamin A derivatives such as the RX gold standard retinoid Retin-A, as well as its over-the-counter version, retinol, to boost long-term collagen production and spur cell turnover. Over time, this proven anti-ager keeps skin lifted and pores at their smallest. However, be warned: those with sensitive skin can see redness and flakes. Start by using sparingly every other night, then wait three days to gauge how skin reacts; mix with a cream if you see any sign of irritation.
The Product:&nbsp;<a href="http://bit.ly/1pN5GH8" target="_blank">SkinMedica Tri-Retinol Complex</a> ($55) contains three forms of OTC vitamin A along with a sustained-release delivery system that helps lessen irritation.
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UV radiation contributes to 90 percent of skin aging. And that includes a loss of elasticity. "The earlier the skin&rsquo;s support structure is compromised, the sooner pores will become bigger," says Dr. Brandt.
The Fix: Slather on sunscreen 365, rain or shine. While burning UVB rays are present during summer months and in warm climates, UVA (the deeply penetrating, aging rays) are present year-round and responsible for breaking down collagen. Look for a label that specifically touts broad spectrum coverage (the new FDA rule means that the company went through rigorous testing to be able to legally put that term on the bottle).
The Product:&nbsp;<a href="http://bit.ly/1oH8iHc" target="_blank">Miracle Skin Transformer SPF 20</a> ($48) uses silicone and light reflecting mica to diffuse the appearance of pores temporarily.
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Makeup, dirt and debris can cause pores to expand. Especially when gunk is literally pushed inside&mdash;like when you hit the gym or the sack with a face full of makeup.&nbsp;
The Fix:&nbsp;No matter how tired, don't skimp on your nightly cleaning regimen; and always wash your face before working out, not just after. Make sure to exfoliate once or twice a week to remove dead skin cells as well as leftover debris. If you have sensitive skin try a non-abrasive exfoliant such as a lactic, salicylic or glycolic acid; if you can tolerate a physical scrub, manually buff with a grain-based treatment.
The Product:&nbsp;<a href="http://www.boots.com/en/Soap-Glory%C2%99-Fab-Pore%C2%99-2-in-1-Facial-Pore-Purifying-Mask-Peel_1364144/?affwin&amp;awc=2041_1412367888_7abffa36ce623779d61efbc11456d871&amp;cm_mmc_o=-uubkbzfwlCjCKww5kbELCjCvi%20i9%20niioCjCC" target="_blank">Soap &amp; Glory The Fab Pore mask</a> ($25) uses exfoliating salicylic acid to break down excess skin cells to dislodge oils trapped below.

You've examined them in horror in magnified mirrors, slathered them with all manner of products and clogged them up during sweaty workouts. Your pores — all three trillion of them — regularly take a beating. On the face alone, most of us have around 20,000 of these minuscule openings and their physiological benefits are largely misunderstood, according to dermatologist Fredric Brandt, M.D., whose clients include Marc Jacobs and Madonna. "Every pore is actually the opening of a hair follicle that’s connected to either an oil gland or a sweat gland," says Dr. Brandt. "Its role is to help pump oil (aka sebum), a natural lubricant responsible for pH balance, up to the skin's surface 24/7; or act as an outlet for sweat, which cools your body temperature down as it evaporates off of skin."So how do you take care of this oil-pumping army? While their appearance and function is in large part determined by your DNA, Brandt explains the four key triggers that affect pore behavior and gives his recommendations for combating negative effects in the slideshow above.