On sunny days, many people often flock outside. But it’s common to notice how differently people’s skin reacts to the same amount of sunlight. Some develop a golden tan or even a dusting of new freckles after spending hours outdoors, while others turn red and experience a painful sunburn.
But what causes these reactions? According to Pedram Gerami, a dermatologist and dermatopathologist at Northwestern University, these differences are multifactorial. They are influenced by genetics, skin type, and melanocytes—cells that produce melanin, the pigment that colors skin and helps protect it from ultraviolet (UV) radiation. Understanding these factors helps explain individual responses to sun exposure and underscores the importance of proper sun protection.
UVA vs. UVB Rays: How Sun Exposure Affects the Skin
Basking in the sun exposes a person to UV radiation, which is made up of different types of rays, such as UVA and UVB. The skin’s melanocytes detect UV light and, thanks to their production of melanin, can absorb the UV rays and protect the body. Melanocytes produce two forms of melanin: eumelanin, which is darker and more protective, and pheomelanin, which is lighter and often associated with red or blonde hair.
“When you’re exposed to ultraviolet rays, just from the visual part of it coming into your eyes, it stimulates your brain to release a hormone called pro-opiomelanocortin, which breaks down into smaller molecules, such as [alpha-melanocyte-stimulating hormone]. That stimulates your body's melanocytes all over your body to make more melanin and hence more pigment,” explained Gerami. This response is a defense mechanism.
UVA exposure leads to more immediate tanning, affecting pre-existing melanocytes by oxidizing and darkening existing melanin. Meanwhile, UVB rays trigger melanocytes to produce new melanin, which leads to a delay in skin darkening.1
The Role of Melanin in Skin Color, Tanning, and Burning
One major factor that sets people’s tanning experiences apart is genetics. Skin pigmentation is a sliding scale of varying hues from pale skin to rich deep shades. Because melanin is a naturally protective agent, the more melanin a person has, the darker their skin, and generally more protected their skin is from UV damage.
A key gene involved in pigmentation is melanocortin 1 receptor (MC1R). MC1R provides instructions for producing the melanocortin 1 receptor protein, which is primarily located on the surface of melanocytes.
There are over 100 known variants of MC1R, and certain variants can influence how a person’s skin reacts to UV exposure.2 When skin is exposed to UV radiation, MC1R is activated in melanocytes, triggering melanin production as a protective response. However, certain MC1R variants reduce this response, leading to phenotypes such as fair skin, red or blonde hair, freckling, increased sun sensitivity from more eumelanin production, and poorer tanning ability. Other genes can also contribute to this.3
This increased pigmentation, Gerami noted, is not quite DNA damage, but “it is a harbinger or signal or message about how much UV [radiation] you've received.” He noted that a person’s ability to repair DNA damage is also another factor to consider; a weaker response can result in unwanted mutations and increased risk for melanoma.
Tanning and Sunburns: What’s the Difference?
But just because a person doesn’t burn, doesn’t mean that damage isn’t occurring.
Both tanning and sunburn are responses to UV exposure. A suntan represents the skin’s attempt to protect itself by increasing pigment production in response to injury, whereas a sunburn is a more severe reaction. Excessive UV radiation can overwhelm melanocytes and trigger an inflammatory response, resulting in redness, swelling, and pain. When cellular damage is extensive, affected skin cells die and are eventually shed, which explains why skin peels after a sunburn.
Skin responses to UV exposure are not limited to tanning or burning alone. Some individuals develop freckles. According to Gerami, the freckling response can be related to DNA damage that results in mutations that cause melanocytes to proliferate more. These spots are areas of increased density of melanocytes. “So, I wouldn't call it a precancer, but you are creating increased proliferation of those cells. And the more you keep increasing that, it's not surprising that those patients have a higher risk for getting skin cancer and melanoma.”
Sun Habits and Environmental Exposure Matter for Skin Health
Just as a leopard cannot change its spots, people cannot change their inherent biological responses to the sun. However, they can modify their lifestyle choices, such as avoiding tanning beds, and environmental exposures to reduce risk.
In addition to sun exposure, tanning beds can also amplify a person’s risk of developing melanomas.
Ben Schamisso / Northwestern University
Sun exposure varies significantly depending on time, place, and duration. Avoiding periods when the UV index is highest—typically midday—can reduce UV damage. Location also plays an important role: Higher altitudes receive more intense UV radiation due to thinner atmospheric filtering and lower latitudes closer to the equator experience stronger UV exposure year-round.
Duration and pattern of exposure are equally important. Gerami noted that many patients report being diligent with sunscreen use throughout the year, only to experience severe sunburn during a single vacation.4 This highlights the importance of consistent sun-protective behaviors.
“If you look at the epidemiologic correlation of UV exposure and melanoma, there are actually two different patterns that correlate with getting melanoma.” One pattern reflects the cumulative UV exposure over a person’s lifetime.
“But then there's another pattern which is more related to having these tense intermittent bouts of sun exposure. You don't necessarily have to be getting it consistently. Just a few of these bad experiences where you get a very intense dosage, bad enough to burn you, those are very significantly related [to melanoma].”
So, the next time the weather is bright and sunny, it’s important to practice good sun protection—using sunscreen, wearing protective clothing, and limiting time in direct sunlight. Whether a person’s skin tans easily or burns quickly, too much sun exposure can cause damage, making protection essential for everyone.
- Sample A, He YY. Mechanisms and prevention of UV-induced melanoma. Photodermatol Photoimmunol Photomed. 2018;34(1):13-24.
- Dessinioti C, et al. Melanocortin 1 receptor variants: Functional role and pigmentary associations. Photochem Photobiol. 2011;87(5):978-987.
- Visconti A, et al. Genome-wide association study in 176,678 Europeans reveals genetic loci for tanning response to sun exposure. Nat Commun. 2018;9(1):1684.
- Wu S, et al. Long-term ultraviolet flux, other potential risk factors, and skin cancer risk: A cohort study. Cancer Epidemiol Biomarkers Prev. 2014;23(6):1080-1089.
