Hair that gradually shifts toward red, orange, or coppery tones usually signals a change in the balance of pigments inside each strand. Your hair contains two types of melanin: a dark brown-black pigment and a reddish-brown pigment. When something disrupts or removes the darker pigment, the reddish one becomes more visible. This can happen for several reasons, from sun exposure and nutritional gaps to medications and the natural aging process.
The Two Pigments in Every Strand
All human hair gets its color from a mix of two pigments. Eumelanin is responsible for brown and black tones. Pheomelanin produces reddish-brown and yellowish hues. The specific shade of your hair depends on how much of each pigment your follicles produce and the ratio between them.
People with naturally red hair have roughly equal amounts of both pigments. People with dark brown or black hair have far more eumelanin, with only a trace of pheomelanin sitting underneath. That trace of red pigment is always there, even in very dark hair. It only becomes noticeable when something strips away or breaks down the eumelanin that normally masks it.
Sun Exposure Is the Most Common Cause
If your hair turns reddish or coppery during summer months, UV light is the likely culprit. Sunlight triggers a chemical reaction that breaks apart eumelanin molecules. The process works through free radicals and oxygen, which attack the ring-shaped structure of eumelanin and essentially crack it open. Once those dark pigment molecules are degraded, the reddish pheomelanin underneath shows through.
Here’s the key detail: eumelanin is actually more resistant to this kind of photodegradation than pheomelanin. But because dark hair has so much more eumelanin to lose, the visual effect is dramatic. As UV exposure chips away at the dominant dark pigment over weeks and months, you’re left with a noticeably warmer, redder tone. This is why dark-haired people often notice auburn or copper highlights after a summer spent outdoors, especially at the ends of the hair where strands have had the longest cumulative sun exposure.
Nutritional Deficiencies Can Change Hair Color
Protein malnutrition is one of the most well-documented nutritional causes of hair turning lighter or reddish. In severe cases, the hair develops what’s called a “flag sign,” where alternating bands of normal and discolored hair appear along the shaft. Each light or reddish band corresponds to a period when the body didn’t have enough protein to produce normal amounts of dark melanin pigment.
This pattern is most commonly seen in children with kwashiorkor, a form of severe protein-energy malnutrition, but milder protein deficiencies can also affect pigment production in adults. Deficiencies in copper, iron, and certain B vitamins have also been linked to changes in hair pigmentation, since these nutrients are involved in the enzyme pathways that produce melanin. If your hair is changing color and you’ve also noticed increased fatigue, brittle nails, or changes in your skin, a nutritional issue is worth investigating.
Medications That Alter Hair Pigment
Certain drugs can interfere with melanin production in the hair follicle, shifting color toward lighter or reddish tones. Chloroquine (used for malaria and some autoimmune conditions) and cancer chemotherapy agents have the strongest evidence for causing hair color changes. The mechanism varies by drug, but generally these medications disrupt the enzymes responsible for building melanin or damage the pigment-producing cells in the follicle.
Other medications have been reported to cause color shifts, though with less definitive evidence. These include some anti-seizure drugs, certain heart medications, and minoxidil. The color change typically reverses once you stop the medication, since new hair grows in with normal pigment production. If you’ve noticed your hair shifting color after starting a new prescription, that connection is worth mentioning to your prescriber.
What Happens as Hair Ages
The path from your natural color to gray or white isn’t always a clean transition. For many people, hair passes through a warmer, redder phase along the way. This happens because the follicle doesn’t shut down pigment production all at once. Eumelanin production tends to decline first, and the remaining pheomelanin can give individual strands a coppery, strawberry, or auburn appearance before they eventually lose all pigment and turn white.
This intermediate phase is especially noticeable in people who had dark hair to begin with. You might see reddish or warm brown strands mixed in with your graying hair for years before those strands go fully white. People with naturally red hair tend to follow a different trajectory. Their hair typically fades to blonde and then to white rather than going gray, because the pigment fades gradually instead of the follicle abruptly stopping production. Some natural redheads retain pockets of their original color well into their later years, particularly at the back and sides of the head.
Pool Water and Hard Water
If your hair picks up a reddish or orange tint after swimming, the cause is usually mineral deposits rather than chlorine itself. Copper salts dissolved in pool water bind to the hair shaft and can create warm discoloration. The technical term for green-tinted swimmer’s hair is chlorotrichosis, and despite what most people assume, it’s the copper that causes the color change, not the chlorine.
The same thing can happen with household tap water if you have newer copper pipes. Freshly installed pipes lack the protective limescale buildup that prevents copper ions from leaching into the water. Over time, repeated exposure to copper-rich water can deposit enough mineral residue on your hair to shift its apparent color. Regular shampooing and conditioning generally removes the buildup and restores your natural tone, since the discoloration sits on the surface of the strand rather than inside it.
Previously Dyed Hair Turning Red
If you’ve colored your hair in the past, a reddish shift is extremely common as the dye fades. Hair coloring works by first lifting your natural dark pigment and then depositing new color molecules into the strand. The artificial color molecules wash out over time at different rates, and the smaller, cooler-toned molecules (ash, blue, violet) tend to fade fastest. What’s left behind are the larger, more stubborn warm-toned molecules, which is why faded hair dye so often skews orange or brassy.
At the same time, the lightening step of the dyeing process permanently removes some of your natural eumelanin. So as the artificial color washes out, you’re seeing a combination of residual warm dye molecules and your own exposed pheomelanin. This is why people who dye their hair brown or black often see it fade through an auburn or copper stage, and why colorists use toning treatments to neutralize those warm undertones.
When a Color Change Signals Something Else
Most of the time, hair turning reddish has a straightforward explanation: sun, aging, nutrition, or cosmetic history. But unexplained changes in hair color, particularly when they appear suddenly or alongside other symptoms, can occasionally point to hormonal shifts, thyroid dysfunction, or autoimmune conditions that affect pigment-producing cells. A change isolated to hair color alone, happening gradually over months, is rarely a sign of anything serious. A rapid or patchy change, especially combined with hair loss, skin changes, or fatigue, deserves a closer look.