Nobody knew just how three young girls ended up with such serious skin burns they had to be rushed to hospital and hooked up to morphine to manage the pain.

Stephanie Ellwanger from Washington in the US dropped her daughters Jewels, 12 and Jazmyn, 9 off at her mother's place for a pool party along with three of their friends - Reyghan, Candy and Bailey.

The girls spent five hours swimming and playing in the sun.

That night Stephanie noticed redness around the girls' mouths. She applied some lotion, thinking it was sunburn. By the next day, her girls were covered in blisters. She gently washed her daughters in the shower and applied some cortisone cream. On Monday morning Jazmyne said it hurt to talk. The girls condition deteriorated and by Monday morning their mother was seriously concerned.

Stephanie rang the other mothers. All of the children were suffering from what they thought was bad sunburn. One girl was already in the emergency room and about to be moved to a burns ward. Denise Kinser woke to the sound off her daughter Candy screaming in pain.

“It’s the worst sound a mother can ever hear,” she told the Hanford Sentinel. “My little girls crying, saying it hurts, and having no idea what is the matter. No mother should ever go through that.”

By that night all five girls were admitted to hospital with second-degree burns covering 15 percent of their body.

What on earth could have burned these girls so badly?

Stephanie tried to think of what could have happened. Was it severe sunburn? No, they had all been covered in sunblock. Was it the pool water?

The doctors said it must have been some kind of acid. They didn't often see child burns like this. But where would the girls have been exposed to acid?

She then thought of the neighbour's large lime tree that grew over the fence into the backyard next to the pool. The girls had picked some fruit and squeezed them into pretend tea cups and played a game of lemonade stand.

Could limes have possibly caused such horrific injuries? Maybe they'd been sprayed with a pesticide or something. She went home and Googled limes and a word she'd never heard of before came up. Phytophotodermatitis is when a chemical reaction occurs when bare skin with certain compounds on it is exposed to ultraviolet light. The compounds aren't just in limes but in other fruits and vegetables.

“It’s so uncommon and unheard of that the doctors didn’t even consider it,” Ellwanger said. “We had to sit them down at a computer and make them read the articles we found.”

The girls remained in intensive care for three days and stayed in hospital for two weeks. However their road to recover will be a long one. Doctors have recommended the girls stay indoors for six months, maybe longer because they have to stay out of sunlight until they have healed. Some of the damage may even be permanent.

The girls will all be home schooled this year and can go outside in the evening for fresh air, once the sun has set.

Stephanie says her daughters Jewels and Jazmyn have adjusted well to the changes now that they are no longer in pain but she is still devastated for them. They have scars and marks on their hands, faces, legs, arms and torsos.

“I feel guilty. When you send your kids off with another parent, you expect them to come back unharmed. I guess we learn the hard way. Who would’ve known that these innocent little fruits could do so much damage?”

The mums aren't blaming anyone for the situation and have banded together to spread the word on Facebook, asking friends and family to share their story. “If we can prevent this from happening to anyone else, then we want to get our story out there. I feel responsible for what happened. There was no way of knowing, but these girls were still under my care. I don’t want to see anyone else go through what we’ve been through.”