Sometimes eye color may seem to change depending on what color clothes you are wearing or time of day. But real changes in color could indicate an underlying health disorder that needs to be addressed.

“Eyes can appear to change color due to an undiagnosed disease, a new medication or even trauma,” says Dr. David Silverstone, professor of ophthalmology at Yale School of Medicine. It’s important to always have these changes checked out by a medical professional.

Here are some changes to watch for:

• A hazy blue ring that forms around your cornea. According to AARP, this could signal a buildup of fats or lipids in the eye and can be a sign of high cholesterol, especially if it occurs before middle age. The usually harmless condition is called arcus senilis and is often seen in older adults. 

• Loss of pigment. Dr. Davinder Grover, spokesperson for the American Academy of Ophthalmology, says there are certain eye conditions that can cause your eyes to lose pigment over time. One is called pigmentary glaucoma, when the pigment rubs off the back of your iris. It can also happen after cataract surgery.

• Clouding of the lens. Cataracts can cause the eye lens to look milky white, says Silverstone. The National Eye Institute says that a quarter of those in their late 60’s will develop cataracts, while more than one third of people in their 70’s will get them, says AARP.

• Freckles on the iris. According to the American Academy of Ophthalmology (AAO), small brown spots on the surface of the iris are often linked to sun exposure and are harmless. Iris nevi, or large freckles or dark growths in the eye that look like a mole, are caused by pigment cells called melanocytes. They are usually slow-growing and harmless, but could be a risk factor for cancer.

• Dilated pupil. This can make the eye color appear different because less of the color of the iris can be seen. A dilated pupil can be a symptom of a serious condition, such as stroke of brain injury. The formal term for a difference in pupil size is anisocoria, say the AAO. The color difference between musician David Bowie’s eyes was from anisocoria.

• Eye color changes from medications. Using glaucoma medications called prostaglandins can cause permanent eye color changes, making eyes a darker shade of their natural color over time. They can make brown or hazel eyes appear darker, says Grover, but do not normally cause color changes in blue or green eyes.

• Blood in the eye. This condition, called hyphemia, usually comes from an injury or appears after surgery.

• “Black” eye. A blow to the eye can cause tissue loss that can make the eye appear as if it’s a different color. “If the trauma is bad enough, the pupil may stay dilated, which can make the eye appear black,” explains Silverstone. See your doctor for medical treatment.