The 46-year-old admitted he was informed about his hair loss by his old school friends after celebrating scoring twice against Liverpool.
The Wales manager revealed that he initially cut off his locks to hide his thinning hair but remained scared of above-pitch TV cameras showing the world his secret.
Giggs now part-owns the MHR Clinic in Knutsford, Cheshire, where he was treated, along with former England cricket captain Michael Vaughn and hair treatment expert Craig Henton.
Giggs remembered the banter thrown his way after United’s 2-1 win at Anfield in 2003, saying: “We’d won and I was buzzing.
“I walked into the pub later and was expecting to hear ‘Well done’ from my mates and all I got was ‘Flippin’ heck, your barnet’s going’.
“It was a bit of a shock. It was like, ‘cheers lads’. It was one of those.”
Speaking to staff at MHR Clinic, Giggs added: “I got a little bit paranoid, especially when I was going to be playing on TV or it was going to rain.
“I was almost 30 then. At the end of my teens and in my early 20s I had really thick hair, long hair, curls.
“That’s why I started to cut it a bit shorter. I felt the shorter it was, the thicker it looked. It had a big bearing, over the years, on my hair getting shorter and shorter.”
Former Red Devils boss Sir Alex Ferguson was notorious for his appropriately named “hairdryer treatment” after poor performances, adding to the pressure in the United dressing room.
“Football is stressful,” Giggs continued. “You put yourself under pressure. You’re aware of the consequences if you lose a game or don’t play well.
“You are under the spotlight and if you have a bad game you’re aware of the criticism.
“Then it becomes a little bit more stressful. And stress is related to hair loss.”
Giggs, who played 963 games for United, began using lasers, lotions and special shampoos to encourage hair growth on the advice of a clinic in 2009.
He visited MHR Clinic in seven years later to accelerate growth and was so impressed with the results that he bought a share in the company.
Speaking about his treatment, he said: “It was straightforward and lasted more or less half a day. You can have a rest during it if you want.
“They numb the areas where you’re going to feel it but you can’t really feel anything.
“The recovery period doesn’t take long. You’ve got, not scarring, but a few cuts in the back of your head.
“There’s a bit of blood on your pillow for a couple of days and then that goes. That’s it. You go back to the consultant. They take a picture of the area the work was done every month and then you can see real progress.
“At three or four months I was thinking, ‘Is that going to be it?’ but Craig, who I’ve known for a long time and trust, told me ‘No there’ll be more, even up to a year’.
“It’s a little after a year when you see the final results.”
Giggs did not tell his teammates he was undergoing treatment at the time. “Back then people were judging you more than now,” he said.
“I kept a low profile, staying in the house, wearing a cap if I went out. I told friends and family and their reactions were better than I expected. No-one took the Mick or had a joke. They were more inquisitive about what I’d had to do and when I’d get the final results.
“This is the first time my team-mates will be hearing about it.”
Hair-loss treatment is increasingly common now and business is good at MHR Clinic since Craig Henton invited him to become a partner.
“Craig was hungry to make it work. His knowledge in the industry is second to none. For me, it was a no-brainer,” Giggs said.
“The industry was booming. I had someone I could trust and so far it’s gone really well. I think more and more people are going to have the procedure.”
“I didn’t want to talk about it while I was playing. You have enough pressures as a footballer. If you’re a private person it can be stressful too.
“There’s still a sort of stigma for men but in the last ten or 20 years, it has got better. People understand hair treatments a lot more.
“It used to be just women who had procedures to make themselves feel more confident but now I think it is becoming more and more the same with men.”
Giggs’ old teammate Wayne Rooney was the first household name footballer to reveal to the public his hair transplant in 2011.
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“Wayne was very brave in being so open about it,” Giggs said. “I’m really happy with mine.
“The only negative I have is that I didn’t do it earlier.”
Referee Mark Clattenburg, 44, and BBC weatherman Simon King, 57, are amongst those who have since been treated at Giggs’ clinic.