Sunscreen 101

Sunscreen is a topical application, commonly as a lotion, spray, or gel, that absorbs or reflects some of the sun’s ultraviolet radiation.  The use of sunscreen is of particular importance due to the effects that excess solar radiation has on the skin, which include mild effects such as sunburn and photodermatitis, or severe impacts such as melanoma and other forms of skin cancer. UVA (ultraviolet A) and UVB (ultraviolent B) rays are the major components of solar radiation that can damaging effects on the skin.

Penetration of UV Radiation

UVA is an abbreviation for long wavelength ultraviolet A radiation, while UVB is an abbreviation for medium wavelength ultraviolet B radiation.  UVA and UVB rays penetrate the various layers of skin.  Though UVA is more abundant and known to penetrate deeper layers of dermis (skin) than UVB, it is typically more benign than UVB.  UVA rays cause damage to the basal and squamous layers of the skin (see photo) and is a major contributor to wrinkling (photoaging) and skin aging, as well as carcinoma in the cells of the aforementioned skin layers.  Tanning beds can expose the skin to approximately 12 times the amount of UVA radiation than that of the sun.  UVB rays do not penetrate as deep as UVA rays but cause the same effects, such as photoaging (wrinkling) and skin aging, as well as cause the most malignant form of skin cancer, melanoma.

UVA = 400-320 nanometers UVB = 320-290 nanometers UVC= 290-100 nanometers

SPF is an acronym for Sun Protection Factor and is a label used to indicate how well the product will protect an individual’s skin from burning due to extended sun exposure.  SPF is determined by using the equivalent of noontime sun indoors and determining how long it takes an individual’s skin to burn using SPF or not using SPF.  SPF often refers to protection from UVB, though certain active ingredients in sunscreen also protect against UVA rays.

A simple way to determine how long you can be exposed to sun before you ‘burn’ with sunscreen is to multiply the SPF factor by the amount of time it takes your skin to burn without sunscreen.  Therefore, if it takes your skin 15 minutes to burn without sunscreen and you wear SPF 45 sunscreen you can be exposed to sun for 675 minutes (11 hours and 15 minutes) without burning when applying the recommended amount of sunscreen.  It should be noted that sweating and water exposure decrease the effectiveness of the sunscreen and therefore should be reapplied as recommended.  The amount of time it takes skin to burn will vary based on skin color.  Darker skin tones have the best natural protection from the sun and take significant time to ‘burn’, whereas pale skin has very minimal protection and burns easily.


The most commonly used active ingredients in sunscreen that absorb UVA and UVB radiation include titanium dioxide, zinc oxide, oxybenzone, avobenzone, dioxybenzone, and aminobenzoic acid (PABA).  Most these active ingredients provides protection from UVB though some also protect from UVA, or only from UVA radiation.  Clothing can offer sun protection, depending on thickness though it typically does not exceed and SPF of 6.  Various natural ingredients (oils, butter, etc.) offer low SPF protection as well.


Thank you for reading!  If you have any questions or comments, please feel free to share in the comments!


One thought on “Sunscreen 101”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s