A 14-year-old girl from Bedfordshire with a nut allergy had to go to hospital after a kiss from a boyfriend who had eaten a cereal with hazelnuts.
A trace got in to Laura Kukic's system at school and her face swelled up and breathing became difficult in minutes.
Staff injected her with adrenaline and she made a full recovery before returning home to Barton-le-Clay.
The experience has prompted her to warn other youngsters who may have the same condition that a kiss can be dangerous.
She said: "Who'd have guessed that a peck on the lips could be so dangerous?"
The incident happened last month after the Year 10 pupil arrived at Harlington Upper School.
She met her then boyfriend before lessons began.
She said: "It was just a friendly hello kiss. Nothing out of the ordinary, nothing passionate just a brief touch of the lips."
Laura was first diagnosed with a severe nut allergy when she was three years old and has to carry her 'EpiPen' around with her wherever she goes.
The allergy means that any contact with nuts, however slight, can bring on a severe reaction.
Her face swells up, her throat tightens and it is hard for her to breathe as she undergoes a reaction known as anaphylactic shock.
"I hadn't noticed anything, but my boyfriend could see that my face was starting to swell, so that my head looked visibly bigger.
"Then he said 'Oh, I did have cereal with hazelnuts in, but that was about and hour ago, and I've brushed my teeth and had a drink, surely that will be alright'.
"Then he said 'Your head appears to look fatter, surely you can't be that sensitive'.
"I thought he was being cheeky," she said
Laura realised that after kissing him she'd also taken a sip from his can of coke which could have been contaminated with a slight trace of nut.