She wrote: "For all the new baby mummy's that might be losing some hair after birth, I'm right here with you, I think it's starting to slowly grow back, so it's all good guys!! Embrace it, and let's enjoy being with our beautiful little cuties!"
The photo showed Jossa's hair in a long plait, with thinning hair around her forehead.
Speaking to HuffPost UK Parents, Women's health specialist and nutritionist Marilyn Glenville said: "For some women this can be frightening because it seems like a lot of hair is falling out.
"But it only looks a lot because in pregnancy you lose less hair due to higher levels of oestrogen.
"After birth, when oestrogen drops, this hair is lost quickly. But after a few months, this evens back out to where you were pre-pregnancy."
Jossa's post - which racked up 21,000 likes - caused many other mums to become open about their own hair loss stories.
Not only that, the conversation with hundreds of comments included women offering tips to each other on how they dealt with it.
One mother wrote: "I've lost looooooads. Tips... Hairburst tablets to help grow back quicker, 'growitgirl' hair root spray and nioxin shampoo to help new follicles come through easier.
"I've tried everything out there and these 3 have seemed to work".
Another mother offered encouragement: "I lost so much hair when my baby was around 4/5 months I went to the doctor!
"Don't worry everyone it grows back, my baby is 14months now and I have about 3 inches of growth in the areas I lost it. Main n tail shampoo helped."
The actress gave birth in February to her and her fiancé Dan Osbourne's first child together.
Not long after posting the photo of her hair, the new mum uploaded a sleep photo of her daughter on the "hottest day of the year".
She added: "Weather is too much for this dramatic little bubba!"