Eye color is determined by genetics and cannot be changed by environmental factors like sunlight exposure. However, some research suggests that increased UV exposure may cause a minor lightening of eye color in people with lighter eye colors like blue, green or hazel eyes. This effect is temporary and does not represent a true change in genetics.
What determines eye color?
Eye color is primarily determined by the amount of melanin pigment in the iris of the eye. Melanin is produced by cells called melanocytes. The number, size and distribution of melanocytes in the iris determines eye color.
People with brown eyes have a large amount of melanin in their irises, while people with blue eyes have much less melanin. Green and hazel eyes fall somewhere in between.
The amount of melanin present is determined by genetics. The OCA2 and HERC2 genes located on chromosome 15 are the main genes responsible for eye color. Different versions of these genes result in varying amounts of melanin.
Can sunlight alter genetics?
Sunlight and ultraviolet (UV) light cannot alter genetics. Exposure to UV light does not change the DNA sequence of the OCA2 and HERC2 genes that determine eye color.
Some exceptions include radiation at extremely high levels, like X-rays, which can damage and mutate DNA. But the UV rays from sunlight do not cause significant genetic mutations or changes.
Can sunlight lighten eye color?
While sunlight cannot genetically alter eye color, some research indicates that increased UV exposure may temporarily lighten eyes over time by degrading melanin pigment:
- A 1969 study found that Syrian hamsters exposed to UV radiation had a slight decrease in iris pigmentation after 4 weeks. The effect reversed once UV exposure ended.
- A 2002 study found a subtle lightening effect in human donor eye tissue exposed to high-intensity UV light over several weeks in vitro.
- A 2010 study of C57BL/6 mice found less melanin production in eye tissue exposed to UVB light for 6 weeks.
However, these lab studies used UV exposures much more intense than what people receive from sunlight. So it’s unclear if sunlight has the same effect.
Who may experience lightening from sunlight?
Some research suggests sunlight exposure over many years may cause subtle lightening of lighter eye colors like blue, green and hazel:
Blue eyes – A 1980 study of fresh eye tissue found some degradation of melanin when blue eyes were exposed toUVB light over several weeks. This indicates blue eyes may be more susceptible to lightening from sunlight.
Green eyes – A 1990 study proposed that sunlight degrades the yellowish pheomelanin pigment more than dark brown eumelanin in green/hazel eyes, shifting them to a more blue appearance over time.
Hazel eyes – A 2012 study suggested that higher lifetime UV exposure is associated with lighter-colored eyes among Caucasians. This was not seen in African-Americans with darker brown eyes.
However, these effects appear very small and slow. One study estimated lightening of 0.3% over 50 years of sun exposure. Most changes are imperceptible without precise measurement.
Is the sunlight effect permanent?
Any lightening of eye color due to sunlight appears to be very subtle and reversible. Avoiding sunlight would likely return any minor color change back to normal within weeks to months.
This is because sunlight does not alter genetics. It may only temporarily degrade some melanin, which can be restored once sun exposure is reduced.
Conclusion
Genetics fully determine true eye color that remains fixed throughout life. Sunlight and UV exposure cannot alter the DNA sequence of the genes responsible for eye color.
However, some research indicates sunlight may temporarily and reversibly lighten lighter eye colors like blue, green and hazel by degrading small amounts of melanin. This effect is likely very subtle and slow over decades. It does not appear to significantly lighten the darker brown eye color of most populations.
So while sunlight cannot genuinely change eye color in a meaningful way, limited data suggests those with lighter eyes may experience a very small and imperceptible lightening effect over a lifetime of sun exposure.