What Causes Cataracts? Ageing, Diabetes, Steroids, Injury and More
By Pauline Driscoll | Medically reviewed by Mr Lewis Pereira, FRCOphth
Published March 30, 2026 · Last reviewed April 8, 2026 · 2 min read
Key takeaways
- Cataracts are mostly age-related; lens proteins clump over the years, and most people have some clouding by their 70s.
- Diabetes is a major risk factor and can bring cataracts on earlier and faster than ageing alone.
- Long-term steroid use, particularly oral steroids, is a recognised cause of cataract.
- Eye injury, previous eye surgery, UV exposure, and smoking all raise the risk of cataract.
- Some cataracts are congenital, present at birth or in childhood from genetic conditions or infections in pregnancy.
Cataracts are mostly age-related: over the years the proteins in the eye’s natural lens clump together, so the lens clouds and yellows, and most people develop some degree of clouding by their 70s1. Beyond ageing, the recognised causes include diabetes, long-term steroid use, eye injury, ultraviolet exposure, smoking, and some genetic conditions, with a minority of cataracts present from birth2.
Knowing what drives the clouding helps make sense of the wider picture. For the condition itself see what is a cataract, for the warning signs see cataract symptoms, and for the only treatment see cataract surgery.
Ageing: the main cause
Ageing is by far the main cause of cataract1. The natural lens is made of carefully arranged proteins, and over decades those proteins clump together, scattering light and tinting the lens yellow or brown. This is why most people have some lens clouding by their 70s and why cataracts are the leading cause of reversible blindness worldwide3.
In my own case there was no dramatic trigger at all. My sight had simply dimmed over years, so gradually that I had adapted around it without noticing. That slow, ageing-related clouding is the typical story, and both my eyes were affected.
Diabetes and metabolic causes
Diabetes is a major risk factor and can bring cataracts on earlier and faster than ageing alone, because raised blood sugar alters the lens2. People with diabetes are advised to keep blood sugar well controlled and to attend regular eye checks, as they face other eye risks alongside cataract.
If this applies to you, our companion piece cataracts and diabetes goes into the relationship in more detail, including why eye monitoring matters.
Steroids, injury and other medical causes
Long-term steroid use, particularly oral steroids over months or years, is a recognised cause of cataract2. Eye injury and some previous eye operations can also trigger a cataract, sometimes years later, and these can affect a single eye at any age. Other eye conditions, including glaucoma, can sit alongside cataract.
The practical message from clinical guidance is that if you take regular steroids or have had an eye injury, your eyes should be monitored so any lens change is found early4. Never stop prescribed steroids without medical advice.
Lifestyle, UV and congenital causes
Among lifestyle factors, smoking and long-term ultraviolet exposure from sunlight are both linked with a higher risk of cataract, which is why UV-blocking sunglasses are a sensible precaution2. None of these outweighs ageing, but they are within your influence.
Finally, a minority of cataracts are congenital, present at birth or in early childhood, often from a genetic condition or an infection in pregnancy1. These are picked up at newborn checks and need prompt specialist care. Cataracts appearing unusually early in adults are covered in cataracts in younger people.
References
- Cataract surgery, NHS. ↩
- What causes cataracts?, American Academy of Ophthalmology. ↩
- Blindness and vision impairment, World Health Organization. ↩
- Cataracts in adults: management (NG77), NICE. ↩
Common questions
What is the main cause of cataracts?
Ageing is by far the main cause. Over the years the proteins in the eye's natural lens clump together, so the lens gradually clouds and yellows. This is why most people develop some degree of lens clouding by their 70s, and why cataracts are the leading cause of reversible blindness worldwide. It is a normal part of how the eye ages rather than a disease you have caught.
Can diabetes cause cataracts?
Yes. Diabetes is a major risk factor and can bring cataracts on earlier and more quickly than ageing alone, because raised blood sugar affects the lens. People with diabetes are advised to keep their blood sugar well controlled and to attend regular eye checks, since they are also at risk of other eye conditions alongside cataract.
Do steroids cause cataracts?
Long-term steroid use, particularly oral steroids taken for months or years, is a recognised cause of cataract, and inhaled or topical steroids can contribute at higher doses over long periods. If you take regular steroids for another condition, it is worth mentioning at your eye checks so any lens changes are picked up early. Do not stop prescribed steroids without medical advice.
Can an eye injury cause a cataract?
Yes. A blow or penetrating injury to the eye, and some eye operations, can trigger a cataract, sometimes years after the original injury. These are called traumatic cataracts. They can affect one eye only and can appear at any age, which is one reason cataracts are not solely a condition of older people.
Does sunlight cause cataracts?
Long-term exposure to ultraviolet light from the sun is considered a contributing risk factor for cataract, which is why wearing sunglasses that block UV is a sensible precaution. UV is one of several lifestyle factors, alongside smoking, that are linked with a higher risk, even though ageing remains the dominant cause.
Can babies be born with cataracts?
Yes. Cataracts can be congenital, meaning present at birth or developing in early childhood, often from a genetic condition or an infection during pregnancy. Congenital cataracts are picked up at newborn eye checks and need prompt specialist assessment, because untreated cataract in a developing eye can affect how vision develops.
Can cataracts be prevented?
There is no guaranteed way to prevent age-related cataracts, but you can reduce some risk by not smoking, protecting your eyes from UV with sunglasses, managing diabetes well, and using steroids only as prescribed. Regular sight tests mean any cataract is found and monitored early, so treatment can be timed around your daily life.
Written by Pauline Driscoll. Medically reviewed by Mr Lewis Pereira, FRCOphth.
Our guides are written from personal experience and reviewed by a qualified clinician for accuracy. Read our editorial policy.
More from us
Cataract Surgery and Dry Eye: Pre-existing Dryness, Drops, and Comfort After · Cataracts in Younger People: Steroids, Injury, Diabetes and Congenital Causes · Cataract Myths and Facts: What Is True and What Is Outdated · Cataracts in One Eye: Imbalance, Anisometropia, and When to Operate · Cataract Surgery With Macular Degeneration: A Good Op, Honest Expectations