Addison's disease, also known as primary adrenal insufficiency disorder , is a rare adrenal gland disease. Its worldwide incidence is only 6 out of 1 million, primarily affecting females in their 30s to 50s. Adrenal glands are two small, triangular glands located above the kidneys. Like other glands, they produce hormones, particularly cortisol and aldosterone. Addison's disease affects the cortex (the outer layer) of the adrenal glands, stopping the normal production of these hormones. As a result, the patient's body encounters deficiency of the adrenal hormones, followed by a series of physiological reactions. Types of adrenal insufficiency There are 2 types of adrenal insufficiency: primary and secondary. The difference is in their disease processes and hormones affected. Primary adrenal insufficiency (Addison's disease) . It is caused by the direct destruction of the adrenal glands. The most common aetiology is autoimmune diseases, meaning the body's immune cells attack their own's body tissue. Secondary adrenal insufficiency . It may happen in people taking an extended period of steroids. Cortisol itself is a steroid hormone that is naturally produced by the adrenal glands. When there are external steroids that are like cortisol, the body reacts by the pituitary gland (the major command centre for hormones, which lie just beneath our brain) reducing production of ACTH – the hormone that will act on the adrenal gland to command it to produce cortisol. As such, if ACTH is suppressed, the adrenal glands go to sleep and stop producing cortisol.