Sister's pic has Twitter in hysterics

Why you should keep away from poison ivy. Photo / Twitter

A teenager earned the wrath of her older sister after posting an unflattering image of her face, swollen from an allergic reaction.

The photo was posted on Twitter, and was promptly retweeted 40,000 times, but one person didn't think it was funny.

According to BuzzFeed, Emily Petrozza, 21, from Connecticut in the US, developed a rash from poison ivy that started off as a small patch of irritation on her arm.

DONT GET POISON IVY ON YOUR EYES pic.twitter.com/yy9oOf2sHM

— Laur (@lauren_petrozza) June 13, 2016

She wasn't too worried, until the rash started to spread to her face, leading to eyes so swollen she struggled to open them.

"I didn't recognise myself," she told BuzzFeed. "I could see a little bit but my eyes were so swollen that it hurt to keep them open.

After bursting into tears at the sight of her swollen face in the mirror, Emily enlisted the help of a friend to take her to the doctor.

Before leaving the house, her 17-year-old sister, Lauren, took a quick snap.

Emily took one look at her face and burst into tears, but her sister found it hilarious. Photo / Twitter

Lauren uploaded the pic to Twitter, and it wasn't long until the internet was laughing about Emily's misfortune.

40K people are laughing at my sister

— Laur (@lauren_petrozza) June 14, 2016

"When I got that picture, I just started dying laughing," Lauren told BuzzFeed. "I just thought it was hilarious."

The sisters, minus a poison ivy reaction. Photo / Twitter

Emily was given a course of medication and is now much better. She's taking all the attention in her stride and has apparently forgiven her sister.

-nzherald.co.nz