The question of whether eye color can change is complex, depending on if the change is a genuine alteration in pigment or merely a shift in appearance. The color of the iris, the muscular ring that controls the pupil, is generally stable throughout adulthood. True pigment changes are rare, occurring naturally during early development or in response to specific medical conditions. More commonly, the perception of eye color shifts due to changes in light, pupil size, and surrounding colors, creating the illusion of a transformation.
How Eye Color is Determined
The color of a person’s eyes is determined by the amount and distribution of a single pigment: melanin. This dark brown substance is also responsible for the color of skin and hair. The iris has two main layers, and the quantity of melanin in the front layer, known as the stroma, dictates the final color.
Brown eyes, the most common color worldwide, result from a high concentration of melanin in the stroma, which absorbs most incoming light. Conversely, blue eyes contain very little melanin in this front layer. The blue appearance is an example of structural color, where light passing through the low-pigment stroma is scattered back toward the viewer. This scattering causes shorter, blue wavelengths of light to be reflected. Green and hazel eyes fall in between, containing moderate amounts of melanin that combine with the light scattering effect.
Natural Changes Over a Lifetime
The most significant and common genuine change in eye color occurs during the first years of life. Many infants, particularly those of lighter-skinned heritage, are born with eyes that appear blue or gray. This is because the specialized cells that produce melanin, called melanocytes, have not yet been fully activated by light exposure outside the womb.
As the baby grows and is exposed to natural light, the melanocytes begin to produce and deposit more melanin into the iris stroma. If a child is genetically programmed to produce a large amount of melanin, their light-colored eyes will darken, often turning hazel, green, or brown.
While the color of the iris may largely settle by around nine months to a year, minor refinements and subtle darkening can continue until a child is up to six years old. Once the eye color is set in childhood, it remains stable for decades for most people.
Environmental and Physiological Factors That Affect Appearance
For adults, the sensation that eye color shifts is usually due to factors that change how the iris is viewed, rather than a change in the pigment itself. Ambient lighting is the most impactful element, as different light sources contain varying wavelengths and intensities. Bright sunlight can intensify the color of light eyes, while low indoor lighting may cause them to appear darker or more muted.
A major physiological factor is the size of the pupil. When the pupil dilates, it gets larger, exposing less of the surrounding iris and making the eye appear darker overall. Pupil size is constantly changing in response to light levels, emotional states, and focus.
The resulting change in the ratio of the black pupil to the colored iris can make the eye color seem more vivid or different, especially for those with lighter eyes. Colors of clothing or surrounding objects can also subtly reflect onto the eye, creating a temporary optical illusion that alters the perceived hue.
Medical Reasons for Pigment Alteration
Actual, permanent alterations in iris pigment in adulthood are rare and frequently signal a medical issue. One documented cause of true darkening is the use of certain glaucoma medications, such as prostaglandin analogs. These eye drops stimulate melanocytes to increase melanin production, causing the iris to slowly change to a darker brown color. This darkening effect is often permanent and is more pronounced in eyes with mixed colors.
Physical trauma to the eye can also lead to a noticeable color change by damaging the iris tissue. This damage can result in a loss of pigment or a change in the tissue structure, causing the injured eye to appear lighter or display an uneven coloration.
Certain inflammatory conditions, such as uveitis, involve inflammation of the middle layer of the eye and can cause the iris to lighten or change color. Any sudden, unexplained, or asymmetrical change in eye color in an adult warrants an immediate consultation with an eye care professional.