Sunscreen vs. Sunblock - what's the difference?

In my extensive research I found this answer to this question to be concise yet not uncomplicated due to the controversy over the use of some sunscreen formulations. 

Titanium Dioxide and Zinc Oxide are physical sunblockers that protect you from both UVA and UVB radiation from the sun, and are found in most mineral cosmetics to aid in prevention of further sun damage.  They work by preventing the sun from burning the skin through their light refracting properties, basically by reflecting light back, away from the skin.  Mineral powders are ideal and, in my opinion, are an added bonus and the best way to protect your face from further sun damage.

Sunscreens are typically UVA and UVB absorbers and rarely are able to protect you from both types of radiation.  This is the short story, but the explanation is far more extensive.

Chemical sunscreens only protect you from one or the other of these rays and have been found to simply be less effective than physical sun-blockers. This is why you will see them used in combination with each other so that a broad spectrum sunscreen can be accomplished.

However, the level of safety of a chemical sunscreen still remains unclear and their level of effectiveness is argued that many of the chemically formulated sunscreens simply do not hold up and begin to break down in a matter of minutes to hours once exposed to the sun.

We are advised to be wary when it comes to claims made by companies that produce sunscreens as their claims are not always proven and their hype exceeds their official SPF rating. Plus, since these are a chemical absorber of ultraviolet rays, this creates concerns of free radical damage and metabolic changes to the body.

Also, be aware sunscreens can degrade within the tube or bottle and should be discarded each year and new one purchased for maximum effectiveness. Also keep your sunscreen out of the sun and away from heat exposure as this will further degrade the product.

Unfortunately, the FDA has yet to propose guidelines for stability of sunscreens, and I personally have yet to find a sunscreen with titanium and zinc combined, yet I have found zinc or titanium mixed with chemicals with different UVA and UVB sun protection, such as... 

• Avobenzone (UVA – yes, UVB – no)
• Cinnamates (UVA – no, UVB – yes)
• Salicylates (UVA –no, UVB – yes)
• Oxybenzone (UVA – yes, UVB – no)

... fill the gap in skin protection against the suns’ harmful rays.

The one concern for me is Avobenzone in particular, due to its’ ability to absorb UV radiation was studied and shown to convert this light energy into free radical changes causing further damage to the skin. Plus this ingredient begins to degrade within 1 hour and becomes completely ineffective.

The real kicker for me is the FDA has not made any requirements for companies to protect us against UVA radiation, which is astounding since these harmful rays make up 90% of the ultraviolet light that reaches the earth. UVA rays cause premature aging due to deeply penetrating the skin tissue and in high doses can suppress our immune system. It is left up to the manufacturer to provide the UVA level of protection needed.

You may be wondering “what’s the answer?” Well, the answer, unfortunately, is not simple. With due diligence by reading ingredient labels, always try to locate a sunscreen using either Titanium Dioxide or Zinc Oxide within the formulas. Without these, you just are not getting the level of sun protection needed to protect you from UV damage. And until the FDA brings about some criteria needed for sun safety, we are on our own for protecting ourselves. To date the FDA has only approved 17 ingredients for sun safety, while the European Union has approved 29.

The sunscreens / sunblockers I have found to date utilizing minerals for sun protection will be quite spendy as compared to purely chemical sunscreens.  But in comparison to their stability in staying power, they will outlast any chemical sunscreen you use.

Reference for sunscreen information provided by: Diffey BL; Grice J; "The influence of sunscreen type on photo-protection," Regional Medical Physics Department, Dryburn Hospital, Durham, U.K. The British journal of dermatology, 1997 Jul, 137(1):103-5. and the Mayo Clinic and Skin Deep Data Base.

Kenneth A. Arndt, MD, clinical professor of Dermatology at Harvard Medical School, Boston, wrote in the current "Bottom Line Personal" that sunscreen and sunblock are not the same.

Sunblock is opaque and blocks almost all of the sun's UVA and UVB rays. It consists largely of zinc oxide and titanium dioxide. Sunblock does not have to be reapplied every few hours.

Sunscreens are less visible on the skin and are designed to protect against UVA, UVB, or both. They do allow some radiation through and need to be reapplied every few hours because their ingredients break down after exposure to sunlight. If you use sunscreen, it is better to use one that has a high SPF, put on a lot, and reapply every two to three hours.

The best way to keep your skin young is to avoid excessive sun damage, and establish the habit of wearing sun protection. The days of baby oil and iodine are over.

Have a fun summer!