"When I would break out, I couldn't look at myself in the mirror for a couple of months at a time," she told Seventeen.
"I remember doing my makeup before school in the dark, which is an awful idea, but it's because I didn't want to see myself in that bright light."
Cystic acne is the most severe form of acne, occurring when hair follicles are blocked by oil and dead skin cells leading to infection and inflammation. It's characterised by large, deep, painful spots that can't be treated by traditional, over the counter methods.
The 21-year-old says that although she's come to embrace the condition – often making light of it on social media – a bad breakout can still remind her of those darker days.
"Sometimes when I have a breakout it triggers me back to that time when I was a teen and I feel so self-conscious – like the whole world is looking at my bad skin," she said. "I've definitely not gone out of the house because of a breakout, which is horrible.”
The star receives plenty of kudos from fans for her brutal honesty about breakouts.
"I'm still growing up – my body's still changing. Maybe my acne will go away eventually, but for right now, I try to acknowledge it," Lili said. "And poke fun at it in a way, as much as I can. At the end of the day, I tell myself that if I’m walking down the street or having lunch, other people don’t give a sh*t what my skin looks like – it’s just me who cares."
Recently she shared a hilarious photo on her Instagram stories, showing her smiling and makeup-free with little blobs of white cream dotted on her face. The caption: “Tinder profile: Hi I'm Lili. I'm 21, a Virgo, Cali-Girl 😝And I have cystic acne. Hmu.”