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Outdoor vs. Indoor Exposure: The Difference

You’ve probably heard this common media statement: “One indoor tanning session is like an entire day at the beach? It’s a misleading statement. The statement assumes that because the UV intensity of indoor tanning units is greater than that outdoors, the skin is automatically overexposed.

Here’s where the statement goes wrong: Intensity alone isn’t the whole picture. When determining exposure, the formula is:

INTENSITY x DURATION = TOTAL EXPOSURE

Let’s look at it this way:

INTENSITY

The average low-pressure tanning unit intensity is approximately 12 mw/cm2. (Milliwatts per square centimeter is one way to measure the intensity of energy emitted by the equipment.) By contrast, the intensity of the average noon summer sun in the Midwest is 4-5 mw/cm2. Obviously, the intensity of the indoor tanning unit is greater than that of the outdoor Midwest sun.

DURATION

But consider that even though the intensity of the indoor unit is greater than the outside intensity. The time spent in the unit is far less than the time most people spend in the sun. Time spent in the indoor unit is 5-20 minutes. Outdoor duration, however, is much more variable. One might spend five hours on the golf course or an entire day on the beach. Usually we spend considerably more time at our outdoor activities than we spend in a tanning unit.

TOTAL EXPOSURE

Remember, total exposure (the total amount of energy received) is a product of both intensity and duration. Since the indoor dosage is designed to be a sub-burning dose using a formula that says you will not sunburn based on your skin type and exposure schedule, indoor total exposure is likely to be less indoors than outdoors.

The important thing to remember when comparing indoor UV exposure to outdoor UV exposure is this: What matters is how much total exposure you get, NOT how fast you get it.