What Are Autoimmune Diseases and How Do They Start

Why this matters

Understanding what autoimmune diseases actually are, rather than just knowing a condition name, makes it easier to understand why certain symptoms occur, why monitoring matters, and why treatment works the way it does.

What autoimmune disease means

In a healthy immune system, a process called self-tolerance prevents immune cells from attacking the body's own tissue. In autoimmune disease, this tolerance breaks down. The immune system begins producing antibodies or immune cells that target specific tissues as if they were foreign threats. Which tissue is targeted determines the condition. In rheumatoid arthritis it’s the joints. In lupus it can be multiple organs including the kidneys and skin. In Hashimoto's thyroiditis it’s the thyroid gland.

How they start

Autoimmune diseases rarely begin with a single identifiable cause. They typically develop through a combination of factors over time. Genetic predisposition creates a susceptibility but not a certainty. Many people carry genes associated with autoimmune conditions and never develop them. Environmental triggers, including infections, significant stress, hormonal changes, or exposure to certain substances, can activate the immune dysregulation in someone who is genetically susceptible. The two together create the conditions in which autoimmune disease develops.

The process is also gradual. Autoantibodies, the immune proteins that target the body's own tissue, can be detectable in blood years before symptoms appear. This is why some people receive positive blood test results without a clinical diagnosis yet, and why the diagnostic process can feel so prolonged.

Why having one increases risk of another

Because autoimmune disease reflects a pattern of immune dysregulation rather than a single event, having one condition increases the likelihood of developing others. Shared genetic susceptibility, overlapping immune pathways, and the inflammatory environment created by one condition can all contribute to the development of a second. Common examples include thyroid disease alongside lupus or rheumatoid arthritis, and Sjögren's syndrome alongside other connective tissue diseases.

What you could do

• If there’s a family history of autoimmune conditions, mentioning this to the clinical team is relevant as it informs screening decisions
• Track any new or changing symptoms over time, particularly if they feel different from the established pattern of a known condition, as this can signal new immune activity worth investigating

This article is for general information purposes only and doesn’t constitute legal, financial or benefits advice. For advice specific to your situation, please speak to a qualified professional or contact an organisation such as Citizens Advice, who may be able to assist you further.

References:

‘Development of autoantibodies before the clinical onset of systemic lupus erythematosus’ (2003) https://doi.org/10.1056/NEJMoa021933

‘Heterogeneity of autoimmune diseases: pathophysiologic insights from genetics and implications for new therapies’ (2015) https://doi.org/10.1038/nm.3897

‘Recent insights in the epidemiology of autoimmune diseases: improved prevalence estimates and understanding of clustering of diseases’ (2009) https://doi.org/10.1016/j.jaut.2009.09.008