Main Line Center for Skin Surgery
191 Presidential Blvd, Suite LN24
Bala Cynwyd, PA
Phone: 610-664-1414 
Fax: 610-572-7262


Sunscreen 101

Why use sunscreen at all?

Sunlight is composed of visible light, ultraviolet and infrared radiation.

Ultraviolet B can cause sunburn and skin cancer through direct damage to skin cells. 

Ultraviolet A penetrates deeper into the skin and causes damage to the collagen framework of your skin resulting in wrinkling.


A brief history of Sunscreen


1928: First sunscreens emerge

  • Benzyl salicylate 
  • Benzyl cinnamate 

Mid-1940’s: red petrolatum used in WWII
1943: p-aminobenzoic acid (PABA) patented

Sunscreen Terminology

UV = ultraviolet
MED = “Minimal Erythema Dose” Smallest dose of UV radiation that can induce redness of the skin


What is SPF?

SPF = “Sun Protection Factor = MED with sunscreen/MED without
It is a rough measurement of the amount of time that one can stay in sun without burning after using sunscreen and depends on your skin type. For example if you usually get red after 10 minutes of sun exposure, it would take 40 minutes (four times longer) to get red if you used an SPF 4 sun block.

What’s in a sunscreen?

Sunscreens are made of different chemicals that either absorb or reflect ultraviolet (UV) radiation from the sun. Chemicals that absorb UV light breakdown and lose effectiveness over time.

Organic filters absorb UV light:

  • Salicylates : UVB
  • Benzophenones (oxybenzone): UVB with minimal UVA
  • Dibenzoylmethanes (avobenzone): UVA
  • Terephthalylidene dicamphor sulfonic acid (Mexoryl SX, ecamsule)- UVA, photostable

Inorganic filters reflect UV radiation:

Metal oxides (zinc or titanium): UVB and UVA

How much SPF is enough?

Above SPF 30-33, effectiveness of sun block begins to plateau:

  • SPF 15 filters 94% of UVB radiation
  • SPF 30 filters 97% of UVB radiation
  • SPF greater than 30 has more potential for irritation than extra protection

What is “Broad spectrum”?

  • Defined as protection against both UVA and UVB
  • SPF number reflects UVB protection only
  • No current standard exists for reporting or labeling for UVA protection

How to apply sunscreen: How much and how often?

  • First use enough to get the full SPF value on the bottle
  • This means one ounce (a full shot glass) should be applied liberally to all sun exposed parts of the body: twice as much as the average consumer usually applies!
  • Sunscreen should be applied every morning and reapplied every 2 hours while in the sun
  • No sunscreen product is truly water-or sweat-proof!  Reapply after swimming, sweating, or towel-drying
  • Discard sunscreen products after three years or after their labeled expiration date

Is sunscreen enough for sun protection?

  • Don’t rely on sunscreen for complete protection from harmful rays
  • Wear tightly woven clothing and broad-rimmed hat
  • Avoid sun between 10am and 4pm

New Sunscreen Labeling Requirements

On August, 2007, the FDA mandated the following changes for sunscreens to be implemented within 18 months:

  • Change SPF from sun protection factor to sunburn protection factor
  • Mandatory directions regarding “liberal” application and frequency of sunscreen application
  • Addition of avobenzone as combination product with other inorganic and organic active ingredients
  • Revision of UVB labeling system
  • Changes Highest SPF available from 30+ to 50+
  • Addition of 4 star rating system for UVA protection

    1 star: low UVA protection
    2 stars: medium
    3 stars: high
    4 stars: highest available OTC

  • Addition of warning on sunscreen bottles:

    “UV exposure from the sun increases the risk of skin cancer, premature skin aging, and other skin damage. It is important to decrease the UV exposure by limiting the time in the sun, wearing protective clothing, and using a sunscreen”

Frequently Asked Questions:

  1. Does the use of sunscreen decrease vitamin D synthesis?

    Yes. UV radiation, especially in UVB range, activates cutaneous vitamin D synthesis. However, sun exposure with daily activities, or dietary intake of 5-10µg of vitamin D will be enough for most healthy people. Those with Vitamin D deficiency can take safe and effective supplements.

  2. Are combination products with sunscreen and insect repellent safe and effective?

    No. There is decreased efficacy of individual products when they are combined. In addition there are different recommendations for the frequency of re-application: Sunscreen should be reapplied every 2hrs while insect repellant only needs to be reapplied every 6hrs (regulated by EPA). Over use can lead to increased absorption and even toxicity especially in young children.