Green tea is well known for its positive effects on every organ of the body, and it appears to help with acne as well.
Catechins, the polyphenols found in green tea, have powerful anti-inflammatory effects and help reduce skin inflammation. There is also evidence of them being effective against the most common acne-related bacteria. 
In a 2016 double-blind study on 80 people, the patients treated with green tea extract for 4 weeks saw significant reductions in lesions located on the nose, chin and around the mouth. 
But that’s not everything.
Green tea also contains L-theanine, an amino acid known for its relaxing properties. Theanine is commonly used as an anti-anxiety supplement, reducing stress and improving sleep, a usage justified by scientific studies. 
Bad sleep and stress are both factors in acne breakouts: they have terrible effects on your skin.
When you are stressed, your body releases a hormone called cortisol. Cortisol is useful, but especially when it’s chronically at high levels, it causes inflammation, favoring acne breakouts.
That’s the reason acne tends to break out at the worst time! If you are stressed (or ironically, worried about breaking out…), your cortisol levels rise, and your acne is more likely to flare up.
Quality sleep is even more important for your skin. The processes to repair and keep the skin’s metabolism at its optimal pace are regulated by hormones produced during deep sleep, when new collagen is synthesized to keep the skin elastic.
Sleeping badly causes the skin to lose elasticity and overall less healthy.
And of course, stress and bad sleep often come together: stress makes for bad sleep, making you stress even more, and so on.
By acting as a natural relaxant, the theanine found in green tea helps ameliorate the effects of stress, and promotes better sleep.
Luckily, green tea is readily available both in drinking form and, for higher dosages, as supplement.