Six month-old George Dent had a misshapen head which alarmed his mum Charlotte so much she took him to hospital.
But doctors dismissed her fears and discharged George. Not convinced, Charlotte, 22, from Fazakerley, Liverpool, posted a picture of her son on Facebook.
The picture was seen by another mum who told Charlotte that George had a condition that could potentially leave him brain damaged.
The woman said her own son had the same ridge as George running down his forehead and told Charlotte it was a tell-tale sign of the rare condition trigonocephaly.
Charlotte and George's dad, car factory worker Adam Knowles, immediately took their son to hospital where, this time, his condition was correctly diagnosed.
Charlotte told the Liverpool Echo: "My son is six months old and I found out that he has something quite rare.
All the doctors I've been to see and even the health visitors haven't picked up on this. It was a mum whose son has the same thing. If she hadn't got in touch he could have ended up severely brain damaged.
"All I want to do is raise awareness so other people can notice it and get something done before it's too late."
When baby George was born, it was thought his different head shape could be a sign of Down's Syndrome but when he was checked by a pediatrician at Liverpool Women's Hospital it was dismissed and he was discharged.
After being warned by the Facebook mum that her son could have trigonocephaly, Charlotte contacted a specialist at Alder Hey Hospital and received the diagnosis the same day.
The condition is caused when the frontal part of the skull fuses together to produce a head shaped like the bow of a ship.
Charlotte said if the condition goes unnoticed it can cause blindness, severe learning difficulties and in worst cases even death.
"When he was diagnosed I was absolutely devastated, not only with the diagnosis but he will need a major operation at one year which will leave him with a scar from ear to ear which he will have for life," she said.
And if it hadn't been noticed by this woman I dread to think what he would have gone through and what his life would have been like.
A spokeswoman for Liverpool Women's Hospital said: "We always take concerns relating to care provided by this Trust very seriously and where appropriate we will investigate thoroughly."
Good luck with the op! Lovely to hear of Facebook being used as a supportive community.