Fact: Pores don't open or close. The size of your pores depends primarily on your genes and your skin type can play a role too. Naturally dry skin tends to appear poreless, while oily skin often has more-visible pores. You can't physically make them smaller, but what you can do is make them appear smaller. Here's how.
Clean pores will look smaller than clogged ones. Regular facials will deeply cleanse your skin, which you can then maintain with at home facial washing. One of the best professional treatments on the market at the moment is Lisa Harris's Clear + Brilliant Laser Rejuvenation, from £220. It's non invasive and clinically proven to help even out your skin tone and improve smoothness and texture which reduces the appearnace of your pore size. It's a bit pricey but the results are well worth it and can last months on end.
When it comes to DIY, exfoliating is crucial to remove pore enlarging dead skin. If your skin is sensitive, only do it three times a week. Choose an exfoliator containing alpha hydroxy acids, retinol, salicylic acid or fruit enzymes (they break down the 'glue' that holds dead skin cells to increase cell turnover which unclogs the pores, making them appear smaller) rather than something too abrasive which will leave micro tears in the skin.
Always cleanse your face twice. The first time will take off the top layer of dirt, while the second will get in deeper. When you cleanse, consider doing it with a power brush, like the Clarisonic Mia, £99; it uses sonic frequency of more than 300 movements per second to remove more makeup, dirt and sebum than cleansing with your hands does.
Sun damage can actually thicken your skin which will lead to pores looking larger. It also weakens your dermal structure by sapping collagen, elastin and water from your skin which causes the walls of your pores to sag and look more visible. Make sure you apply an SPF daily or use a moisturiser containing sun protective qualities like Eau Thermale Avène Hydrance Optimale UV Light SPF20, £14.50.
Oily skin can not only clog your pores, it also reflects light which makes them appear bigger. Apply a mattifying moisturiser or serum, such as Clarins Truly Matte Pore Minimizing Serum, £27 which contains oil-absorbing ingredinets like Alpine Willow Herb to keep shine at bay.
Try to encourage the production of collagen and elastin as well to give structural support to your skin. IPL (Intense Pulsed Light therapy) and LED (light-emitting diode) can make pores look smaller. The light reaches deep into the skin to stimulate collagen production without harming the surface layer.