Sun Harm
Sunlight is actually comprised of several different types of ultraviolet radiation, some which are more harmful than others. Skin exposure to such radiation causes cellular DNA damage – contributing to the build-up, or directly causing improper mutations which lead to the progression of skin cancer. The US Environmental Protection Agency (EPA) has estimated that UV radiation from the sun alone is the cause of nearly 90% of all non-melanoma skin cancers. In addition, excess sun exposure has also been associated with increased skin wrinkling, inflammation, and sun burns.


Sunburn Risk Factors
Some risk factors of skin cancer include lighter-skinned individuals, living near the equatorial areas, and having a positive family history of skin cancer. Other bodily traits which increase skin cancer risk include having blond or red hair, blue eyes, and having a greater number of skin moles.
Age is also another oft-ignored fact in sun exposure. Young children as well as the elderly have thinner skin layers, and thus require enhanced levels of sun protection. It has been observed that suffering from one sunburn in childhood or adolescence doubles the risk of melanoma in life, and that five sunburns by any age doubles this risk as well.

Both chronic and intermittent intense exposure have both been shown to increase the risks of skin cancer.
Some medications may also increase sun sensitivity – including antibiotics like the Tetracyclines, Fluoroquinolones, NSAID pain relievers, and Retinoids (acne medications).


Sunscreen Types
Sunscreens’ protective strengths are classed by SPF (sun protection factor), a number denoting the increased time of sunburn resistance compared with wearing no sunscreen. SPF 15 is recommended for everyday use, while SPF 30 is recommended for days of intense sun exposure.

For adequate protection, everyone over the age of 6 months should use sunscreen daily in all weathers. Infants should always be kept out of the sun or completely protected with clothing or umbrella).
It should also be noted that overcast days also pose a UV threat, with up to 80% of UV rays passing through both clouds and fog.

Sunscreen ingredients fall into two categories: physical screens and chemical absorbers of UVR. Physical blockers are regarded as superior, and these can be identified with ingredients including Titanium dioxide and Zinc oxide.
Chemical sunscreens are less messy but provide less protection. Examples of partially blocking chemical agents include the Cinnamates, with Octinoxate being the most commonly used.



Application
Sunscreen should be applied 30 minutes before going outside, and should be re-applied after 2 hours use or in water exposure or heavy sweating. An amount equal to two tablespoons is usually needed to cover the entire body, with thicker applications needed for areas with thinner skin such as the face.
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The rule of 9’s can be referenced on how to apply adequate amounts to each body part. With approximately 35ml needed for the average adult body, this simple diagram can aid in determining distribution requirements.
It is also crucial to re-apply to skin after water exposure, and to completely cover all areas including the bottoms of feet.
If multiple skin products are to be used, the sequence of application is also of importance. For best results, the individual skin products should be applied 15-30 minutes apart to allow for adequate absorption. If a moisturizer and separate sunscreen are used, the moisturizer should go on first, followed by sunscreen, and then makeup. If topical medication preparations are being used, they should be applied before everything else, and allowed to absorb before applying the other skin preparations.

The value of proper sunscreen use cannot be understated – one research study from Australia demonstrated that invasive melanomas were reduced by 73% with daily SPF 16 sunscreen exposure.
Other protective measures include avoiding direct sunlight between 10AM-4PM, and wearing protective clothing, hats, and UV blocking sunglasses.
Also of note, is the fact that UV tanning beds are equally if not worse than natural sunlight, and should not be used for sun tanning. If a tan is absolutely desired, spray on tans are recommended.

References:
Patient Self Care, 2nd Ed. Canadian Pharmacists Assoc; (July 29 2010).