Ann Quinlan said her limb looked like something from an ‘apocalyptic horror film’ after she swept past the plant on a dog walk in north London.
But the poisonous plant was only diagnosed by a junior doctor who Googled her symptoms.
The 56-year-old was left with fist-sized blisters that have turned into weeping sores doctors warn could take months to heal.
Still housebound over a week later Ann described her ordeal at home in Enfield, north London.
The dog lover had taken her rhodesian ridgeback and two chihuahuas for walkies through parkland at Forty Hall, where she has walked her pets for 18 years.
She said: “I’m quite into my gory films, this was just like when everyone catches a deadly virus. When I look back at the photos I’m just shocked.
“It was a nice day so I had my shorts on and I decided to take the route through a wooded area.
“This time of year it’s quite overgrown, I did brush up against a few plants, but I had no idea I was supposed to be looking out for anything.”
That evening she noticed her legs and hand begin to tingle and burn, but put it down to a bit of sunburn.
She went to bed at around 9pm after trying slathering her leg in Sudocrem and yoghurt to ease the heat.
She continued: “I couldn’t understand and by about 4am I was in agony, it was very red, the redness was spreading from the top of my thigh down my right leg. Then I noticed the little blisters starting to appear.”
By 5am Ann’s concern was so great she decided to go to hospital and was driven to North Middlesex Hospital by her partner.
She faced a worrying two-hour wait in A&E before being given a bed in the acute ward, although staff were puzzled by her symptoms. Her terror grew as the redness, blistering and discomfort increased.
Her burns were originally diagnosed as cellulitis, an infection of the skin.
It wasn’t until midday that hog weed was identified as a culprit – by a student doctor in her early 20s who put her symptoms into Google.
Ann was “plonked” on a monitoring ward with eight other patients and prescribed antibiotics, steroids and codeine to deal with the pain.
“It was so painful, like bad toothache but in your leg. A pulsating, throbbing pain that was enough to make me feel nauseous,” she said.
Throughout the start of the week the pustules continued to grow.
“It was worst when I had to go to the toilet, they were so big they dragged and pulled on my skin.”
She had also suffered some burns to her left leg and right hand, that left it too painful to move her fingers.
Ann has been left needing regular hospital checkups, takes 14 tablets a day and endures the pain of dressing changes on the raw wound left on her leg.
Doctors warned it may take months to heal and could be weeks before she can return to work.
Ann said she contacted Enfield Borough Council to alert them to the weed’s presence when she was discharged last Thursday.
“It’s the summer and kids want to go outside, but no-one wants to have to cover up,” she said. “We need to be aware of the plants, maybe signs showing which are dangerous would be useful.”