A friend told the Daily Mail how the 34-year-old woke up 10 days ago to find clumps of her hair had begun falling out.
She said: At first she went into denial and hid herself at home - she didn't want to go out or see anyone.
But eventually she went to see her doctor and he told her she is suffering from alopecia.
Initially she cancelled all her appearances and said she wasn't going to go out to LA to do her new TV show. But now she has decided to face her demons and she's determined not to let this beat her.
Edinburgh-born Porter recently filmed Dead Famous Lives for the satellite entertainment channel Living TV.
The former Big Breakfast and Top Of The Pops presenter famously had a picture of her naked body projected on to the Houses of Parliament in 1999.
She was admitted to hospital in March after taking an overdose of post-natal depression tablets.
She has a two-year-old daughter, Honey, with ex-husband and Toploader guitarist Dan Hipgrave. The couple split up last year after three years of marriage.