Sunscreen
“Keep your face to the sun and you will never see the shadows.”― Helen Keller.
I would add- but please wear sunscreen first.
The Sun’s ultraviolet rays are a constant presence on the earth. The need to protect from harsh
sunlight has been recognized since long. Human exposure to ultraviolet (UV) radiation from sunlight
is known to cause adverse effects.
UVB radiation (290-320 nm) is mainly responsible for the most severe damage: acute damage, such
as sunburn, and chronic damage like skin cancer. It has a direct impact on cell DNA and proteins.
UVA radiation (320-400 nm) is not directly absorbed by cells, but yet can dramatically impair cell and
tissue functions. UVA penetrates deeper into the skin than UVB.It particularly affects connective
tissue where it produces detrimental reactive oxygen species (ROS). ROS cause damage to DNA,
cells, vessels, and tissues. Photosensitivity reactions and photodermatoses are primarily mediated by
UVA.
It is important to note that under any meteorological conditions, UVA irradiance is at least 17 times
higher than UVB irradiance. For all these reasons, it is evident that sunscreens must contain both
UVA and UVB filters to cover the entire range of harmful radiation.
Sunscreens have been divided into chemical absorbers and physical blockers on the basis of their
mechanism of action. Chemical sunscreens are generally aromatic compounds conjugated with a
carbonyl group. This general structure allows the molecule to absorb high-energy ultraviolet rays
and release the energy as lower-energy rays, thereby preventing the skin damaging ultraviolet rays
from reaching the skin. So, upon exposure to UV light, most of the do not undergo significant
chemical change. This allows these ingredients to retain the UV-absorbing potency without
significant photodegradation, thereby preventing the skin-damaging ultraviolet rays from reaching
the skin. Physical blockers or non chemical sunscreens reflect or scatter UVR. They contain inert
minerals such as titanium dioxide or zinc oxide.
An appropriate sunscreen product should provide effective protection against both UVB and UVA
radiation, must be stable to heat and to UV-radiation (photostable), and should be cost-effective and
userfriendly to encourage frequent application and provide reliable protection. To protect against
both UVB and UVA, it must contain a combination of active ingredients (either organic or inorganic)
within a complex vehicle matrix. Active ingredients can act either by absorption, or reflection or
diffusion of UV radiation (UVR).Organic ultraviolet filters are active ingredients that absorb UVR
energy to a variable extent within a specific range of wavelengths depending on their chemical
structure. The control of filter behavior under UV exposure is a critical issue that needs to be
thoroughly investigated when new sunscreen products are developed.
Practicing dermatologists often encounter patients complaining of worsening pigmentation or
recurrent polymorphous light eruption in spite of using sunscreens with “good sun protection factor
(SPF)” or “SPF >50”. It is important for both dermatologists and the public to be aware that a good
SPF value will not protect the skin from the entire UV spectrum. In fact, in 2007, the FDA has
proposed that the expansion of SPF be changed to “sunburn protection factor” to indicate that it is
only an index of protection against sunburn or UVB-induced erythema, and hence does not
necessarily imply UVA or broad spectrum protection
Grading system for SPF: • Low: SPF 2 – 15 • Medium: SPF 15 – 30 High: SPF 30 – 50 • Highest: SPF >50
Note: It is noteworthy that a sunscreen with an SPF of 15 blocks about 93% of UVB radiation, while
one with an SPF of 30 blocks about 97% of UVB radiation. This difference of 4% may make the
difference between an aesthetically pleasing sunscreen and an undesirable one, as products with
higher SPF generally tend to be uncomfortable due to the higher concentration of the active
ingredient.
Most individuals do not apply enough sunscreen to achieve adequate protection. It has been found
that 20-50% of the required amount of sunscreen is usually used by most individuals. To cover the
average 1.73 m2 adult, approximately 35ml of sunscreen is required. The teaspoon rule of applying
sunscreen is as follows: Apply slightly more than ½ teaspoon (~3ml) to each arm, to the face and the
neck. On each leg, the chest and back, apply slightly more than a teaspoon (~6ml).Using an adequate
amount of sunscreen (2 mg/cm2) provides greater sun protection than using an inadequate amount
of a sunscreen with a higher SPF rating. Patients should select broad-spectrum sunscreens that
contain agents that effectively block both UVB and UVA rays with an SPF of 30 or greater. A
sunscreen with a SPF of 15 filters out approximately 94% of the UVB rays. One with a SPF of 30 filters
out 97%. The SPF applies for UVB rays only. The protection provided against UVA rays in chemical
sunscreens is about 10% of the UVB rating.[26] Natural pigments such as titanium dioxide and zinc
oxide are good UVB and UVA blockers. Today, certain chemicals can be added to sunscreen products
to give them good UVA ray blocking abilities. Such chemicals include avobenzone and Mexoryl SX.
Foundation makeup products without sunscreen may not offer more than a SPF of 4 via its pigment
content. However, most of cosmetic products that contain sunscreen chemicals offer various SPF
levels up to 15-30.
Sunscreens alone may provide insufficient protection from UVR as they prevent sunburn from UV-B
radiation and provide more limited protection from UV-A radiation. Avoiding solar exposure at times
of peak intensity, using cover-up garments and sunscreen lotions is an effective combination for
protection of the skin on sunny and cloudy days.
Sunscreen should be applied properly to all sun exposed areas (in a concentration of 2 mg/cm2 ),
and allowed to dry completely before sun exposure. It should be reapplied every 2 hours, and after
swimming, vigorous activity, excessive perspiration, or toweling.