Sunscreen « Return to Eden Blog

Sunscreen FAQ January 28, 2010

Filed under: FYI,Sunscreen — returntoedencosmetics @ 3:26 pm

I was planning to post a comprehensive blog on sunscreens and the information for and against their use and which ones are best to use. But, with the overwhelming amount of contradictory information available on sunscreens, I felt a blog post on the subject would add to the confusion rather than provide clarity. So, I decided to offer some general information on sunscreen instead and have included several links for you to visit for additional information.

1) What does SPF mean?

Let me say this first (and repeat it throughout) – SPF is only a measure of UVB protection and not UVA protection.

SPF or sun protection factor is determined by the difference in the amount of time it takes skin to burn (as determined by the erythema – redness of the skin) with sunscreen on vs. the amount of time it takes skin to burn when no sunscreen is worn. That being said, most sunscreens contain a combination of sunscreen ingredients to provide both UVA and UVB protection.

2) What is the difference between UVA and UVB?

UVA are also known as the aging UV rays. Their wavelength is 400–315 nm and these rays are more penetrating than UVB rays meaning they are not inhibited by atmospheric phenomena (i.e. clouds, particles, etc.) as much as UVB rays and therefore are more likely to reach the skin. These rays are the primary contributor to melanoma.

UVA does not cause direct DNA damage (as UVB does) but rather generates free radicals and reactive oxygen species and reactive carbonyl species – ROS and RCS, respectively that then cause cell and DNA damage.

UVB rays, also known as burning UV rays, have a wavelength from 315–290 nm. These rays are blocked from hitting the skin by clouds, glass (i.e. car windows), and do not penetrate as far into the skin as UVA rays. However, UVB rays can damage DNA and are responsible for sun burn and can lead to skin cancer (primarily basal and squamous cell carcinoma though UVA can also contribute to formation of these types of skin cancers along with UVB).

3) So, tell me more about UVA and UVB -

While we receive most of our yearly dosage of UVB during the summer (when the sun is more direct with our location), UVA is more evenly distributed throughout the year.

Approximately 80% to 90% of signs of aging are due to UV exposure. UV breaks down collagen and elastin in the skin, promotes formation of free radicals, and causes inflammation of the skin. Because the UVA rays actually penetrate to the dermis (the living layer of skin), the dermis is damaged as well as the epidermis when we’re exposed to UV.

4a) Anatomy of a sun tan -

The body is great at protecting itself. Its natural response to UVA rays is oxidation of existing melanin in the skin (melanin is a great antioxidant). UVB stimulates melanogenesis (production of more melanin) though the tan resulting from this generally takes a couple of days to develop not offering much protection in the mean time.

4b) Anatomy of a sunscreen -

There are two types of sunscreen agents – physical and chemical – this are just names – both groups are comprised of chemicals (don’t fret, despite their reputation, chemicals are NOT inherently bad – our bodies are composed of nothing but chemicals – water, DNA, hormones, the amino acids that form the peptides that form the proteins, vitamins are also chemicals), it’s just that the physical sunscreens protect your body from UV radiation by reflecting and scattering UV rays whereas chemical sunscreens work by reacting with the UV ray releasing lower energy things (i.e. heat, other chemicals, etc. – this is why folks complain that sunscreens make them hot).

So, a physical sunscreen simply reflects and scatters the UV rays and the chemical sunscreen in effect absorbs the UV rays in a chemical reaction releasing other compounds and heat in the process – though this sounds scary, just keep in mind, this chemical reaction is no different in nature than chemical reactions between antioxidants and oxidizing agents (example the chemical reaction of melanin and UVA rays wherein melanin is oxidized by the UVA rays). Many chemical reactions take place within the body naturally on a daily basis. So, don’t let this alarm you.

Now, I am not going to discuss nanoparticles in sunscreens or the results of the chemical reactions that occur from the use of SOME sunscreen agents because although I do have an opinion on the subject, it is based on the very limited amount of information I have had time to wade through.

If you want to learn more about sunscreens, I would suggest the Environmental Working Group site (link XVI below).

5) So, how about that tanning bed?

Um, no, no, no.

Tanning beds actually (apparently) rely on UVA rays much more so than UVB rays to give you that nice glow, so no. See the links below for more info.

6) What causes age spots?

Okay, so, this is an area where I’m still a little spotty (having not found a great explanation of this process to date), but here’s what I’ve been able to piecemeal together.

Cells called melanocytes, which reside in the lowest layer of the epidermis – the layer closest to the dermis – produce melanin in the skin. The melanin is then housed in a vesicle known as a melanosome and is transported to keratinocytes (cells which comprise ~95% of the epidermis). The keratinocytes are essentially dyed by the melanin. Now, there are several theories on age spots:

A) Melanocytes (the melanin producing cells) can be damaged by the sun causing overproduction or underproduction of melanin (leading to age spots or areas of hypopigmentation).

B) I have read (though I no longer have the link to this article and will have to update this post after finding it again) that keratinocytes containing melanin can actually migrate and clump together leaving areas of the skin hypopigmented and other areas hyperpigmented (age spots). I will post the link to this site after I have found it again.

C) As we grow older, the epidermis begins to thin allowing melanocytes to come closer and closer to the skins surface revealing age spots (this seems especially valid if A is also true).

7) So, what’s all the hoopla about antioxidants?

Antioxidants fight free radicals and Reactive Oxygen Species (ROS) and Reactive Carbonyl Species (RCS) the destructive compounds produced by UV exposure. So, whereas antioxidants do not protect from UV radiation (as does sunscreen agents), they do protect from the effects of UV radiation by destroying free radicals and ROS. There is solid scientific evidence showing that anti-oxidants protect against erythema (redness induced from sunburn) and protect DNA from damage – see the link to the book excerpt (XIII below).

In addition to commonly recognized antioxidants – vitamins A, C, & E, green tea extract, rutin, acai extract, white tea extract, rooibos extract, ginkgo biloba extract, and coenzyme Q-10 – I also use the peptide, Diaminopropionoyl Tripeptide-33 in a few products – Toujours Jeune Illuminating Light Day Cream and Toujours Jeune Radiant Face & Eye Cream Treatment. Granted, the following images are from the manufacturers of this peptide, but they prove my point – that antioxidants can provide protection against UV induced damage:

Diaminopropionoyl Tripeptide-33