‘Not all sunscreens protect you from uva and uvb’
By Dr Shireen Furtado | Express News Service | Published: 14th March 2018 11:28 PM |
BENGALURU: Keep your face to the sun and you will never see the shadows- said Helen Keller. I whole heartedly agree, provided you wear sunscreen first. The sun’s ultraviolet (UV) light is a constant presence on earth. The need to protect ourselves from the harsh sunlight has been recognised since long, traces of potions having UV light absorbing properties have also been found in ancient pyramids. UV radiation is known to cause several adverse effects to human skin.
Appropriate sunscreen products should provide effective protection against UVA and UVB radiation in addition to being cost effective, photostable, user friendly to encourage frequent application when outdoors, hence providing reliable protection.
As practising dermatologists, we often come across patients who allege that despite using ‘good suncreens’ with ‘high sun protection factor- SPF’ their sun allergy/pigmentation does not improve. This puts one thing in perspective- a high SPF does not guarantee a full UVA and UVB protection spectrum. To increase awareness of this fact, the FDA in 2007, proposed SPF to be called ‘sunburn protection factor’. This indicates that SPF is only an index of protection against UV induced redness in the sunburn. This does not directly imply UVA/ full spectrum protection.
It is of interest that a sunscreen with a SPF 15 blocks 93 percent UVB radiation and one with SPF 30 blocks 97 percent UVB radiation. Products with higher SPF however, tend to be aesthetically less pleasing and uncomfortable to wear.
The other physical factor that makes a difference is the amount of sunscreen applied. Often only 20-50 percent of the recommended amount is used. To cover the avg 1.73 m 2 adult, approximately 35 ml of sunscreen is required. The teaspoon rule of applying sunscreen is as follows:
Apply slightly more than half tsp (3ml) to each arm, face and neck. On each leg, chest, back, apply slightly more than a teaspoon (6ml). Using adequate amount of sunscreen provides more protection than using inadequate amounts of a high SPF sunscreen. A broad spectrum sunscreen, of SPF 30, blocking UVA and UVB would be ideal. Natural pigments like titanium dioxide and zinc oxide are good UVA and UVB blockers. Foundation products without sunscreen may not offer more than SPF 4 via its pigment content. Most cosmetic products that contain sunscreen chemicals offer SPF 15-30 protection.
Source of Vitamin D
UVB radiation is responsible for 90 percent of Vitamin D production in the skin. Of late, there have been debates regarding the rising trend in use of high SPF sunscreens causing a Vitamin D deficiency. There is however evidence to prove that people wearing sunscreen and venturing in the sun have a normal Vitamin D level, when compared to people not wearing sunscreen and remaining indoors in the day.
Avoiding solar exposure at times of peak intensity, using cover-up garments of tight weave and a good broad spectrum sunscreen provides effective cover on sunny and cloudy days.
This article is written by Dr Shireen Furtado, Consultant Dermatology And Aesthetic Surgery.
What is the difference between UVA and UVB?
UV radiation is further divided to UVB (290-320 nm) and UVA (320-400nm). UVB is responsible for acute reactions like sunburn and chronic damage like skin cancer. This radiation has a direct impact on the DNA of skin cells. UVA on the other hand, though not directly absorbed by the cell, can dramatically impair cell and tissue function. UVA penetrates deeper into the skin than UVB and produces detrimental reactive oxygen species (ROS) which cause DNA, cells, vessels and even tissue damage.
Photosensitivity reactions and photodermatoses are primarily mediated by UVA. Under any meteorological conditions, UVA irradiance is at least 17 times higher than UVB irradiance. It is thus evident that sunscreens must contain UVA and UVB filters to cover the entire range of harmful radiation.