Autoimmune diseases develop from a dysfunction of the immune system, where it mistakenly attacks your body.
While some affect specific organs, such as type 1 diabetes, which affects the pancreas, others – like lupus – affect the whole body.
Symptoms vary according to the condition but can include fatigue, rashes and achy joints.
The exact causes remain a mystery, although scientists have several theories.
Genetics plays a part, as does our environment – low vitamin D levels have been shown to be a risk factor for multiple sclerosis.
Certain infections, such as glandular fever, can also trigger an immune response