You’ve probably heard this common mis-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 somewhat greater, the skin is automatically overexposed.

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

Intensity x Duration = Total Exposure

Let’s look at this way:

Intensity: The average 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 around 4-5 mw/cm2. Obviously, the intensity of the indoor tanning unit is somewhat greater than that of the outdoor Midwest sun.

Duration: Now 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. Duration spent in the indoor unit is, on average, 5-20 minutes. Outdoor duration, however, is much more variable. One might spend five hours on the golf course, or even an entire day on the beach. Usually we spend considerably more time at our outdoor activities than the time spent 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 (a schedule developed by the industry in conjunction with federal regulators), indoor total exposure is likely to be less indoors than outdoors.

“So the statement that a tanning session is like an entire day at the beach is completely inaccurate—it is misleading and designed to scare people instead of educate them,” Smart Tan Vice President Joseph Levy said. “We think anti-sun purveyors who spread this misinformation are, in fact, hurting people instead of helping them.”

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