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The sun is that big giant glowing object in the sky. It is a star, like all the tiny glowing objects in the night sky, but we are way up close to it. Extreme pressure caused by gravity compressing a huge mass of hydrogen results in the fusion of hydrogen into helium. A byproduct of that fusion is solar energy. We experience that energy as light. The energy range of solar energy goes from infrared through visible light and into the ultraviolet portion of the spectrum.

Infrared energy is experienced as heat. The sun feels warm on our skin and sometimes even hot. Too much heat, and our bodies have to thermoregulate by reducing activity and by perspiring. This will eventually lead to dehydration if sufficient water is not consumed. There is a section on Hydration in our Guides page which covers this.


Visible light is how we see in the daytime. It is also the energy plants use to photosynthesize. Visible light rarely causes any problems except as reflective glare from water, snow or other reflective surfaces. Sunglasses are effective in reducing glare, especially polarized sunglasses.


Ultraviolet light has more energy than visible light or infrared, and doesn’t really do much for us. It is abbreviated as UV, or UV light. The waves are shorter and so they don’t bounce off of the skin like visible light does. Ultraviolet light causes damage to cells when it penetrates the outer layers of skin. This is called sunburn. UV light can also damage DNA as part of the damage it does to cells. DNA has mechanisms for self-repair, but they are not foolproof, and every once in a while, the DNA is damaged so much that the cell mutates or dies. Cell mutations usually lead to cells being unable to divide, and this leads to the cell dying. Other mutations can become cancers later on.

The symptoms of sunburn are redness and tingling or pressure sensitivity, but that is only in the mildest of cases. It can progress to blisters and breaking of the skin. It can be very painful, and the effects can linger for several days. Sunburn can be merely painful, or it can be debilitating, depending on its severity. In the long term, sun damage can manifest itself many years later, well after your exposure, as freckles, moles, age spots on your hands and face, or even skin cancer. Sunscreen is inexpensive and convenient, and available at almost any store.

The main thing that protects us from the penetrating effects of UV light is the atmosphere. Hiking will sometimes take you to higher elevations like mountaintops and Canyon rims. The high Sierras are over 8000 feet in many places and as much as 14,000 feet at the tops of some mountains. When you get at such elevations, you lose much of the protection of the atmosphere. This means that more ultraviolet light can reach your skin and cause damage.

Fortunately, evolution has led to humans being able to produce artificial coverings for their bodies, which we call clothing. Also, humans have learned to adapt chemical substances to use as skin protectant, and this is called sunscreen. Natural adaptation over millions of years has given us the ability to produce melanin, which is the pigmentation that we call a sun tan. It takes some time and gradual exposure to ultraviolet light to produce a tan, which is somewhat protective. The problem is that it takes some time and planning to become properly tanned before it can be a benefit.

As part of your being prepared, you need to have sun protection. The first item is your hat. A hat protects your head and shades your eyes. It is important that your hat is breathable so that it doesn’t trap a bunch of hot air on top of your head. A cap with a bill is the minimum hat in summer.  A full brim is desirable. Innovations like mesh in the top allow for breathing, and brims with flaps that cover the back of your neck are popular with hikers.

Sunglasses are important protection from UV, as well as visible light, especially near water and snow. Snow is extremely reflective of visible light and ultraviolet light. A condition of excessive ultraviolet light reflecting off of snow into your eyes is called snow blindness. Extremely long-term exposure can lead to cataracts in your older age. Cataracts are a condition of release small fibers going inside the lens of your eye, reducing the amount of light that can get to your retina. This is basically blindness. The treatment for cataracts is replacement of your natural lens with an artificial lens.

Long-sleeved shirts and long pants are excellent protection for the skin on your arms and legs. Gloves can protect your hands. Loose fitting long-sleeved outer shirts over a T-shirt or short-sleeved base layer shirt are a good way to protect yourself. A long-sleeved base layer shirt should be worn when it is warm, and when you are using short sleeves, you must wear sunscreen.

Sunscreen is available in a variety of forms and strengths. A cream a rub on with a high sun protection factor, or SPF, is probably the best option. Aerosol spray is adequate as is a pump spray mist. Sunscreen is also available mixed with insect repellent, which is another important item to carry and which we will discuss in more detail later.
It makes sense to protect yourself from the sun before you experience the damaging effects of ultraviolet light. Wear a hat with a brim. Carry sunglasses and use them. Wear loose-fitting clothing with long sleeves, and light gloves. Always carry sunscreen in your pack, and use it.


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