UV Rays From The Sun

Both ultraviolet A and ultraviolet B radiation damage your skin, but the primary method by which they do their damage is different.

UVB radiation (which is higher energy and has a shorter wavelength than UVA) does the majority of its damage directly to your DNA. When UVB radiation strikes a strand of DNA, it can result in the creation of pyrimidine dimers (either thymine dimers or cytosine dimers). Other names for these structures are cyclobutane pyrimidine dimers (CPDs) and cyclobutane photodimers (CPDs). These unnatural compounds are usually repaired by your skin cells’ natural repair mechanisms, but too much of this damage can result in cell death (as may occur in sunburn), erythema (skin redness), inflammation, and occasionally mutation. Mutations, over time, can cause cancer.

UVA radiation causes its damage via another mechanism. UVA radiation, which is a longer wavelength than UVB and as such can travel deeper into your skin, strikes other structures in skin cells, creating free radicals and reactive oxygen species (ROSs). These free radicals and ROSs can damage your DNA, but they also damage other structures in your skin such as collagen and elastin. This damage eventually results in many of the negative effects attributed to the sun. Furthermore, these free radicals and ROSs can travel through your blood stream and damage other areas of your body not directly reached by UV light.

UVB and UVA rays vary in intensity throughout the day. Because UVB radiation is partially blocked by the earth’s atmosphere, the strength of UVB rays that reach your skin varies considerably depending on the time of day. The further overhead the sun is, and thus the less atmosphere the sunlight travels through before it reaches you, the greater the intensity of the UVB rays. It takes you less time to burn in the middle of the day than the morning or evening.

Conversely, the longer wavelengths of UVA rays are relatively unfiltered by the earth’s atmosphere. The amount of UVA radiation that reaches your skin in the middle of the day does not vary much from the amount that reaches your skin in the morning or evening. Thus, while you may not notice the effects immediately and might not get burned, you are still damaging your skin while exposed to seemingly low-intensity sunlight.

The same holds true when it is overcast, or in the fall/winter/spring. While the intensity of UVB rays is much lower, the intensity of UVA rays remains little changed. While you are not getting sunburned, these periods of sun exposure can be extremely dangerous because the damage being sustained is often unnoticed. These periods of seemingly innocuous sun exposure can significantly contribute to the cumulative damage and aging of your skin.

Color in your skin is primarily attributed to melanin. The more melanin present, the darker your skin. Your body produces melanin in specialized cells called melanocytes. When UVB radiation damages the DNA in melanocytes, creating pyrimidine dimers, melanocytes are triggered to increase their production of melanin. This melanin is released from melanocytes in little packets of melanin called melanosomes, which are eventually taken up by keratinocytes (a type of skin cell). This melanin colors keratinocytes, and as these cells migrate toward the surface of your skin the result is the appearance of your skin as tan. This process of melanogenesis takes 2 to 3 days.

Whereas UVB radiation stimulates your production of melanin, UVA radiation does not. UVA radiation does, however, cause the release of small amounts of preexisting melanin from melanocytes, resulting in an immediate but short-lived “tan.”

The increased production of melanin in your skin is caused by DNA damage from UVB radiation. So, in short, a tan is a marker of some level of DNA damage. However, melanin does protect the skin from additional sun damage by efficiently and harmlessly converting the energy in ultraviolet radiation into heat. The more melanin that is present in your skin, the less ultraviolet radiation is able to pass through to cause damage to other skin structures below it. This same melanin, however, also inhibits your production of Vitamin D.

Ultraviolet B radiation, especially between the wavelengths of 295-297nm, is able to stimulate the production of Vitamin D in your skin. When UVB rays at these wavelengths hit a molecule called 7-dehydrocholesterol (a molecule that would otherwise eventually be converted into cholesterol in the body), it causes the conversion of this molecule into pre-vitamin D3. Over the course of approximately 12 days, this pre-vitamin D3 is converted to Vitamin D3 (also called cholecalciferol), and enters your blood stream. It is then transferred to your liver where it is converted into 25-hydroxycholecalciferol (also called calcidiol) and stored. Eventually it makes its way to the kidneys where it is converted into 1,25-dihydroxycholecalciferol (also called calcitriol): its final, active form.

Vitamin D is involved in a number of crucial pathways in your body, including the proper functioning of your immune system, normal bone growth and repair, the absorption of calcium, the concentrations of calcium and phosphate in your blood stream, neural and muscular function, and the regulation of a number of different genes. In short, it is an extremely important molecule, and production in sunlight is one of the main methods the body obtains its necessary levels of Vitamin D. It is possible, however, to obtain enough Vitamin D from food to meet your needs.

UV rays can also cause the production and release of nitric oxide (NO) in your skin. UVB is able to directly induce the production of nitric oxide via enzymatic activity. UVA primarily releases stored nitric oxide, but can also induce nitric oxide synthases, leading to prolonged NO release.

Nitric oxide is a vital signaling molecule that acts as a potent vasodilator, relaxing and widening blood vessels to improve circulation, lower blood pressure, and boost heart health. It enhances exercise performance, reduces muscle soreness, improves erectile function, and supports immune system function. Key health benefits include:

• Cardiovascular Health: By acting as a vasodilator, NO reduces blood pressure and protects against arterial stiffness and plaque buildup, lowering the risk of heart disease.
• Exercise Performance & Recovery: Improved blood flow delivers more oxygen and nutrients to muscles, increasing endurance and reducing muscle fatigue.
• Sexual Function: It helps treat erectile dysfunction by relaxing smooth muscles to improve blood flow.
• Immune and Nervous System Support: It assists the immune system in fighting bacteria and aids in neurotransmission.
• Metabolic Health: It can help reduce the risk of diabetes complications by improving circulation.

In addition to sun exposure, nitric oxide can also be increased through diet and lifestyle via:

• Diet: The consumption of nitrates in leafy green vegetables like kale, spinach, and arugula, cruciferous vegetables like broccoli, cabbage, and cauliflower, celery, and beetroot, which are converted to nitrites and then nitric oxide in the body. The L-arginine in some nuts and seeds like walnuts, and meat, seafood, and poultry, can also be converted to NO. And foods rich in polyphenols, along with citrus fruits, protect NO from degradation. Garlic also helps increase NO production.
• Exercise: Regular aerobic exercise, resistance training, and high-intensity interval training (HIIT) increase NO production.
• Supplements: L-arginine and L-citrulline are commonly used to support NO production: L-arginine is converted to NO by nitric oxide synthase (NOS), while L-citrulline is converted to L-arginine (to further increase NO production).

While sunlight can give a huge boost to NO levels, diet and exercise may be more consistent and sustainable ways to maintain higher NO concentrations over time.

Ultraviolet (UV) radiation is a form of energy emitted by the sun that is not visible to the human eye. It has shorter wavelengths than visible light and carries more energy, which allows it to interact with the skin and other biological materials. UV radiation is a natural part of sunlight and makes up a portion of the sun’s total energy reaching the Earth.

Ultraviolet radiation is divided into three main types: UVA, UVB, and UVC. UVA penetrates deep into the skin and contributes to aging, UVB primarily affects the outer skin layers and causes sunburn, while UVC is the most harmful but is almost completely absorbed by the Earth’s atmosphere and does not reach the surface.

UV radiation can have both beneficial and harmful effects on the skin. Moderate exposure helps the body produce vitamin D, which is essential for bone health. However, excessive exposure can damage skin cells, break down collagen, and increase the risk of sunburn, premature aging, and skin cancer due to DNA damage in skin cells.

Ultraviolet radiation is typically strongest during the middle of the day, especially between late morning and early afternoon when the sun is highest in the sky. During these hours, the sun’s rays travel a shorter distance through the atmosphere, allowing more UV radiation to reach the Earth’s surface. Even on cloudy days, significant UV exposure can still occur.

Protecting yourself from UV radiation involves limiting direct sun exposure and using protective measures such as sunscreen, sunglasses, and clothing that covers the skin. Seeking shade and avoiding peak sunlight hours can also reduce exposure. Since UV radiation can penetrate clouds and reflect off surfaces, consistent protection is important throughout the year.