Speaking on an episode of 'The Doctors' - which airs in the US - Kelly said: "[Jett] was autistic. He had seizures and when he was very young, he had Kawasaki Syndrome (which can cause inflammation of the arteries and usually affects children between the ages of two and five years old)."
Jett died after suffering a seizure and hitting his head on a bathtub at the family's home at the Old Bahama Bay Hotel on Grand Bahama Island in the Caribbean and his mother believes chemicals caused it.
Kelly said: "I strongly believe as a mother, as does my husband, that there are certain contributing factors that lead to autism and some of it is very much the chemicals in our environment and in our food."
Kelly also blames her difficult "fast and hard" labor for Jett's problems, and antibiotics she took while breastfeeding him, which gave him thrush at the time, an infection of Candida yeast that has been linked by some studies to the symptoms of autism.
Kelly - who is also shares daughter Ella, 12, and son Benjamin, two, with her husband - said she wants to empower other parents and promote an organic lifestyle with fewer chemicals.