So is the former "Eurthymics" singer really ill?
"I can tell you the good news is actually I am not. However, many people are. In fact, 22 million in sub-saharan Africa are currenly HIV positive," Lennox explained on YouTube. "And I am wearing this in solidarity with them because it's very hard when you are HIV postive to be open about your status and to be able to tell your family and your friends."
Lennox is on a mission to fight the stigma surrounding HIV/AIDS, which brings with it "a lot of secrecy and a lot of silence," she added. "What we need to do it to normalize the disease, so it can be just like any other disease."
Had Lennox turned around during her "Idol Gives Back" performance of her new song, "Universal Child," fans' worries would have been wisked away. The back of the T-shirt read, "Fighting HIV/AIDS."
But sadly, not everyone in Africa is so lucky.
Lennox's performance followed footage of a touching story about a 9-year-old girl, Avelile, before and after she received treatment.
Although Lennox wasn't able to attend "Idol Gives Back," due to flight delays from Iceland's volcanic erruption (she appeared via satellite), the Black Eyed Peas, Alicia Keys, Elton John, Carrie Underwood, Joss Stone and Jeff Beck, were among the artists who performed.
In 2007, Lennox founded the SING Campaign. The money raised by SING helps prevent the spread of HIV in South Africa and also supports those currently living with HIV, according to Lennox' official website.
Watch Lennox' performance and her touching trip to South Africa.