Raymond Cuss says the herbal-scented gel stripped a layer off his skin and left him screaming in agony.
The pain was so excruciating it caused him to bend double whenever his underwear simply brushed the affected area.
Raymond Cuss suffered burns to his penis and testicles
The 42-year-old has now received £1,000 pounds in an out-of-court settlement.
The retailer 99p Stores – which has not admitted liability – believes the chemicals in the gel may have reacted with others used by Cuss for his work.
Cuss, who was instructed by a doctor to soothe the inflamed skin by applying moisturiser twice a day, feared he would be scarred for life.
But he has since recovered and there is no lasting physical damage after the incident in August 2011.
Cuss bought the Dettol-branded gel from the High Street branch of 99p Stores in his hometown of Gosport, Hampshire.
Cuss said: "It was the first time I had bought this particular shower gel, and chose it because it had the Dettol brand on the front, which I trusted.
"I had a shower to freshen up when I got home from work and suffered an horrendous reaction.
"When I stepped out of the shower and looked down at my groin I could see I had been burned.
"At that point there was no pain but the area was inflamed, my penis was bright red, and I had lost a layer of skin.
"I was horrified and scared I may have suffered permanent damage. As the area dried, I was left in incredible pain, with a burning sensation.
"I had trouble sleeping, and could not lie on my front because it was far too painful.
"I had tears in my eyes when pulling on my boxer shorts, and if any material simply brushed the area I almost doubled over in pain. I grimaced with every move."
He added: "I went to my local hospital and they said I had suffered burns. I don't have sensitive skin and had never suffered a reaction like this before.
"Because I'm self employed I had to go to work and battle through the pain, which was a real struggle.
"The whole incident left me feeling depressed because I feared my ordeal would never end.
"After a month of applying moisturiser at the doctors suggestion it healed and, thankfully, I have not suffered any lasting damage.
"I don't know what I'll do with the £1,000 but I certainly wont be spending it on shower gel in 99p Stores.
"I now get an even cheaper brand from Lidl."
Cuss entered a lengthy legal battle with 99p Stores after instructing lawyers to act on his behalf.
His solicitor Ian Barnett ordered a medical examination in February last year, which found his skin had completely healed.
In a letter to Cuss, Barnett wrote: "[Distributors Kans and Kandy Wholesale Limited] have come to an agreement with 99p Stores that they will indemnify them for any damages that you may be awarded."
The £1,000 settlement was made before the claim got to court.
Barnett added that the company said: "...the chemicals used during the course of your regular employment may have caused the reaction you suffered when they came into contact with the shower gel.
"By this they mean that ... (normally) the shower gel would not have affected you."
Barnett contacted the makers of Dettol, Reckitt Benckiser, which examined the bottle and directed them to the supplier.
A Reckitt Benckiser spokesman said: "A review of the product packaging identified it as most likely a product originally made for the Korean market and imported as a grey market product."
Cuss said he is pleased that he has now received the cash but still wants an apology.