Showbiz
Rex Features
The supermodel had surgery to remove a cyst earlier in the year and doctors in Brazil said donors must wait six months after having an operation before they can give blood.
"Unfortunately I can't give blood for Rio de Janeiro, but I'll surely be back," Campbell said.
She added that she had seen a TV news report in the UK about a dengue fever epidemic in Brazil and had flown out to offer help.
The disease is carried by mosquitos and can prove fatal if not treated. It has already claimed 83 lives in Brazil with Rio being the worst hit area of the country.
Campbell was recently arrested at Heathrow Airport's Terminal 5 after rowing over missing baggage.
More: Naomi Campbell, Showbiz
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