Sunblock or sunscreen are very important basic skin care products, to protect the skin from UV damage.
They are the first and best line of defence against premature ageing from the sun.
Based on their mechanism of action, sunscreens are also traditionally divided into inorganic (physical) blockers and organic (chemical) absorbers.
SunBLOCK refers to physical blockers, and sunSCREEN refers to chemical absorbers.
Sunscreen chemical absorbers contain substances which are capable of absorbing UV radiation of a specific range of wavelength based on their chemical structure.
These include derivatives of anthranilates, benzophenones, camphor, cinnamates, dibenzoylmethanes, para-aminobenzoates, and salicylates.
Broad spectrum filters used in sunscreen have a higher level of absorption. The organic filter molecules absorb UV energy and transform to higher energy state from the ground state. Excess energy is released via isomerization and heat release resulting in the emission of higher wavelengths or relaxation.
These filters can be photostable, photounstable, or photoreactive.
Photounstable filters are the molecules which undergo degradation or change in their chemical structure on the absorption of UV radiation. Hence, these cannot absorb UV energy on subsequent exposure.
Photostable filters are the molecules which dissipate the absorbed energy to the surroundings in the form of heat. These filters efficiently continue to absorb UV energy.
Photoreactive filters jump to their excited state on irradiation with UV. Once in their excited state, they interact with other molecules in their surrounding including the ingredients of sunscreen, skin lipids and proteins.
This interaction results in the production of reactive species, resulting in untoward biological effects.
Oxybenzone and Octinoxate:
These are chemical sunscreen filters.
Oxybenzone is the most common UV filter used in products worldwide. It is used in almost every foundation and day cream that claims to have an SPF 15.
These chemical filters penetrate into the skin, and absorb the UV rays. The chemical filter will break down within 2 hours by 95%, which is why chemical sunscreens need to be reapplied every 2 hours when in the sun.
When they break down, they increase reactive oxygen species (ROS). This can cause DNA damage which leads to ageing.
Oxybenzone penetrates into the blood stream, lymph system and has been found in breast milk.
Octinoxate absorbs through the skin in significant amounts; A study found Octinoxate in the urine of 97% of americans.
It is associated with photoallergic reactions, and theoretically, endocrine (hormone) disruption can occur.
Ingredients such as phthalates and parabens are also suspected endocrine disruptors – these are found in many sunscreens and other cosmetic products and soaps.
While the systemic absorption of these products and their possible adverse effects are concerns, there is no evidence that they do cause harm in humans; concerns are theoretical only.
It is likely that these ingredients could cause harm if consumed in vast quantities, but not in the amounts we are exposed to by wearing sunscreen.
Oxybenzone can cause endocrine disruption in marine life – including causing sex change in fish.
For this reason, some tourist beaches have policies that visitors must exchange their usual sunscreen for a more biodegradable one.
Inorganic, physical blockers include zinc oxide, titanium dioxide, iron oxide, red veterinary petrolatum, kaolin, and calamine.
These filters block UVB and UVA rays through scattering and reflection.
The larger metal oxide particles tend to diffuse the light from the visible range of the spectrum leaving an undesirable whitish appearance on the skin.
This whitening effect and opaque nature are some disadvantages of these filters, which can be minimised to some extent by the use of ultrafine particles.
Skincare ingredient spotlight: Zinc Oxide:
Zinc oxide and Titanium dioxide are physical filters used in physical sunscreens.
Zinc and Titanium do not absorb into the skin, breakdown or cause endocrine disruption.
They sit on top of the skin reflecting and absorbing UVR like mirrors, and offer broad spectrum protection.
A nanometre is one billionth of a metre. This helps to measure the wavelength of light.
UV rays from the sun range from 290 to 400 nanometers.
The longer the wavelength, the deeper it can penetrate into the epidermis or dermis, causing free radical damage.
Zinc Oxide blocks rays in this entire range, unlike most chemical sunscreens.
Looking at this evidence, physical blockers are far more effective than chemical.
However, no sunscreen or sunblock will be effective if not enough is used, or if it is not used regularly.
How much to apply:
Its advised that we apply 2mg per square cm to our skin. This is around 6 full teaspoons (about 36 grams) to cover the entire body (1/2 a teaspoon for the face) which is the amount used when determining a products sun protection factor.
Studies have found that most people apply less than half of the amount required to provide the SPF level of protection indicated on the packaging.
It should be applied at least 15-30 minutes before going outside.
What SPF to use:
The higher the better. An SPF of at least 30 is advisable, and this should be a broad spectrum sunscreen – protecting against UVA and UVB rays.
400 units (10 micrograms) of vitamin D is the usual daily requirement.
Vitamin D can be obtained from natural food sources, fortified foods, and supplements. Sunlight also helps our skin to produce vitamin D.
It can be difficult to get enough vitamin D from diet alone, which is why deficiency is very common in people who live in countries without much sunlight.
Vitamin D deficiency can cause health issues, so it is important to get enough through supplements or sunlight.
As UV rays can cause skin cancer and premature ageing of the skin, it is best to wear sunblock to the always exposed areas – face neck and hands – every day, and avoid heavy tanning or burning of other areas.
- Look for zinc oxide on the ingredients list – as this is the most effective physical blocker.
- Apply sunblock liberally to all exposed skin, 30 minutes before going outside, 365 days of the year
- Wait a few minutes for the sunblock to set before applying makeup
- Invest in a good broad spectrum, high SPF sunblock to use.
- Wear water resistant sunblock if swimming, and reapply regularly on hot days, if swimming or exercising outside.
- Wear wide brimmed hats when sunny outside.
- Don’t forget hands – reapply sunblock to them after washing them – to keep them looking young too!
- Most people will benefit from a daily vitamin D supplement. 400 units is the usual daily requirement for an adult, but daily supplements of 800-1000 units can be safely taken.