How to Prevent Skin Cancer
To prevent skin cancer, protect your skin from the sun's harmful radiation by wearing hats, long-sleeved shirts, and pants with long legs. Cover any skin that's still exposed with sunscreen that has an SPF of 30 or higher. Do this even if it's cloudy out, since UV radiation can penetrate cloud cover and harm your skin. You can also protect yourself by staying out of the sun between 10AM and 4PM. Finally, avoid risky activities like tanning, and limit your time outside if you're taking medications that might make you more sun sensitive.
Protect yourself from the sun. Take the following steps while outdoors: Wear a hat with a wide brim to shade your head, ears, face, and neck. Cover up to protect exposed skin. Wear long-sleeved shirts and long pants if possible. Note that tightly woven fabrics and dark colors are more protective against the sun. Some clothing will have an SPF value on the label inside to indicate the degree of ultraviolet protection it offers. Try to stay out of the sun when it is most intense, usually between 10 AM and 4 PM. Use sunscreen. Sunscreen with a higher SPF (sun protective factor) such as SPF 30 or higher is best for optimum sun protection. Be sure to apply it on all exposed areas of skin such as your face, your ears, your nose, your chest and shoulders, your arms and hands, your stomach and back, and your legs and feet. Look for a broad-spectrum sunscreen which protects against UVA and UVB rays. Sunscreen should be reapplied every two hours, or after swimming or sweating (such as after a workout). Note that sunscreen should be used even on seemingly cloudy days, as the clouds do not stop the sun's rays from reaching your skin. Try to stay in the shade. Particularly during midday hours (10 AM – 4 PM), when the sun's UV rays are the strongest and can do the most damage, try to stay either in the shade or indoors. The best time to enjoy the sun is in the early morning or the late afternoon, as both of these times are less damaging to your skin when it comes to sun exposure and UV radiation. Protect yourself even on cloudy days. Even if the sun is not shining directly, the UV rays can still pass through the clouds and cause skin damage; therefore, if you find yourself in a warm climate where the sun normally shines but it is temporarily concealed by clouds, be sure to still protect yourself well using sunscreen, a hat, and other precautions. Take extra precaution if you have multiple risk factors. The following is a list of factors that may increase your chances of getting skin cancer: Light skin color History of cancer in the family Prolonged exposure to the sun through work or play History of sunburns as a youngster Skin that burns, freckles, or reddens easily Blue or green eyes Naturally blond or red hair A large amount of moles Skin that becomes painful in the sun An inability to tan Avoid tanning. It is important to know that tanning is also an indication of skin damage. Many people are aware that burning their skin is a warning sign that they have had too much sun; however, few people know that tanning also demonstrates skin damage. Both tanning and burning increase your risk of skin cancer, as well as your total time spent in the sun throughout your life; therefore, limit your time tanning and prioritize the health of your skin by avoiding excess UV rays. Keep in mind that tanning beds and sunlamps emit UV rays. The UV rays from these devices are just as dangerous as those from sunlight, so their use should be avoided. If you want to appear more "tanned," try using a bronzer for your face when you put on makeup, or a bronzing lotion for your body, as this can create the look you are after without risking damage to your skin and possible skin cancer. Be aware of any "sun-sensitizing" medications you may be taking. Some medications carry with them an increased sensitivity to sun damage. One example is the antibiotic doxycycline. Tetracycline, which is commonly used to treat acne, can also cause photosensitivity. Speak to your doctor or pharmacist to see if any of the medications you are currently on affect your sensitivity to sunlight and warrant special precautions. Take note of any new skin lesions. If you notice that a new spot, mole, or other unusual lesion has appeared on your skin, pay careful attention to it. If it changes or grows with time, or appears concerning to you, it is always better to be safe rather than sorry and to consult your doctor to rule out a possible skin cancer. Look for asymmetry. If you find a lesion on your skin that is asymmetrical, it is more likely to be skin cancer or a precursor lesion for skin cancer than one that is symmetrical. This is because cancer cells, as well as precancerous cells, tend to have uncontrolled and uneven growth patterns, often leading to asymmetry. Examine the border of your skin lesion. Is it a smooth and well-defined border, or a jagged and irregular one? Skin lesions with irregular borders are more worrisome, as it can be another sign of the uneven and uncontrolled growth that is a hallmark of skin cancer. Be aware of the size. If the diameter of your skin lesion exceeds that of a pea (or is greater than a quarter of an inch), this is another more worrisome sign. Particularly if the lesion continues to grow and/or change with time, you will want to get it seen by a doctor. Notice the color. Lesions with uneven pigment throughout are of higher risk, as are lesions that are abnormal in color (such as very dark brown, black or blue, or showing irregular shades that vary throughout the lesion). These types of lesions are more likely to be cancerous, and they merit investigation by a physician. See your doctor if in doubt. If you notice risk factors such as those described above when you look at your skin lesion, see a physician who can assess it and let you know whether it is a possible skin cancer. Doctors are specifically trained to evaluate skin lesions, so if in doubt it is always best to get a professional opinion. Understand that most skin cancers are easily curable. Even though the word "cancer" can strike fear in us the moment we hear it, skin cancer is actually one of the most curable forms of cancer. When caught early, it can oftentimes be removed with no long-term ramifications. The key to curability depends on both the specific type of skin cancer, as well as the time-frame in which it is noticed and excised by a physician. If the skin cancer is either a precursor lesion (a precancerous growth), a "squamous cell carcinoma," or a "basal cell carcinoma," it can most likely be removed and cured. These are types of cancers or pre-cancers that, when caught early, rarely cause long-term consequences. Melanoma, on the other hand, is the most dangerous form of skin cancer. Although it is the least common diagnosis, it is the leading cause of death from skin cancer, and the fastest one to metastasize (spread) to other areas of the body. Fortunately, with early identification, many melanomas can be noticed, excised, and effectively "cured" as well; however, the risk is certainly higher with this subtype and thus of greater concern. Biopsy or excise any worrisome lesions. When you see your doctor and show them your skin lesion, they will evaluate it and may recommend biopsying (taking a sample of) or excising (completely cutting out) any lesions that are potential cancers. If your doctor recommends a biopsy or excision, they will most likely send you to a medical specialist (a dermatologist, who specializes in skin concerns) to undergo the procedure. A biopsy is done if the purpose is to gather more information — i.e. if the goal is to determine the specific diagnosis of the skin lesion, and to assess whether or not it is a cause for concern. There are a variety of ways to perform a biopsy; all can be done easily in your doctor's office. An excision is done if the goal is to completely remove the lesion due to a sufficiently high level of suspicion. Generally, skin lesions can be excised using only local anesthetic (local freezing injected in the surrounding skin with a small needle so that you won't feel any pain). It is a procedure that can most often be completed within one office visit, without needing to go to a hospital. If the lesion is smaller, another option is that your doctor may try "cryotherapy," which uses liquid nitrogen to kill the cancerous or pre-cancerous cells; however, this can only be used for lesions that are small and shallow (i.e. that do not penetrate the skin layers too deeply, otherwise the liquid nitrogen is ineffective). Evaluate the "margins" after excision. If you have had a skin lesion excised by a doctor, know that they will examine the piece of skin under a microscope after it has been removed. What the doctors are specifically looking for under the microscope is whether or not the margins (i.e. the borders) are "clear." If the margins are "clear," meaning that they show no cancerous cells, then you and your doctor can take confidence knowing that all of the pathological cells have been removed. On the other hand, if the margins show cancerous cells, it indicates risk that the cancer has spread to other parts of your body and may not have been completely "cured." If the margins show cancerous cells, your doctor will speak to you about how best to proceed, and what further forms of treatment (such as chemotherapy) may be needed to give you the best chance of a complete cure. When surgeons or dermatologist remove suspicious spots, they will generally remove at least 1 cm of normal tissue. This helps ensure removal of all cancerous cell. 
Protect yourself from the sun. Use sunscreen. Try to stay in the shade. Protect yourself even on cloudy days. Take extra precaution if you have multiple risk factors. Avoid tanning. Be aware of any "sun-sensitizing" medications you may be taking. Take note of any new skin lesions. Look for asymmetry. Examine the border of your skin lesion. Be aware of the size. Notice the color. See your doctor if in doubt. Understand that most skin cancers are easily curable. Biopsy or excise any worrisome lesions. Evaluate the "margins" after excision. 