Anne Marie Fox / Focus Features
Matthews had an unheard-of $250 budget to work with for the film which sees the deterioration of AIDS patients Ron Woodroof (Matthew McConaughey) and Rayon (Jared Leto) as their conditions worsen.
Vanity Fair reports Matthews would sometimes transform the two men from healthy to sick - and vice versa - up to five times a day during the film's 23-day shoot.
"When you see them in the film, and they look like they're 25 pounds heavier and healthier because of the medication, that's just makeup," Matthews told Vanity Fair.
The make-up artist referred to the film as the "most under-budgeted movie" she's ever been a part of. The only prosthetic piece Matthews used was a dental plumper to make McConaughey's face appear fuller.
Previously, she has worked on films including "The Twilight Saga: Eclipse" and and "Into the Wild" which had budgets of $68 million and $15 million respectively.
The entire budget for the Focus Features' film is estimated at $5.5 million, according to IMDB.
Without any more money for prosthetics, Matthews told The Hollywood Reporter one of the most difficult parts was convincing audiences of the actor's illnesses as they progressed.
"Mathews explained how the process required hand-painting the rash on Leto's face, topping it off with three layers of grey and marble concentrate, and using a 'stretch and stipple' method to age him. To give the rash a dry, flaky look, Mathews applied another layer made with pieces of grit and cornmeal."
Apparently, Matthews had to borrow the cornmeal and grits from her mom because there wasn't enough money in the budget to purchase either.