No, UPF and SPF are different. The UPF rating is for clothing and the SPF rating is for lotion and other cosmetic products. The UPF rating is applied to textiles that protect your skin from the sun. And while the two are similar, the SPF rating used for cosmetics and sunscreens measures only how much UVB is blocked, but not UVA (unless it is labeled “broad spectrum”). UPF clothing blocks both types of radiation.

If your unprotected skin typically starts burning after 20 minutes, sunscreen with an SPF of 15 would give you 15 times that, or five additional hours. The UPF rating works differently; a garment with a UPF of 50 allows 1/50th of the sun’s ultraviolet radiation, or about two percent of it, to reach the skin through the fabric. By way of comparison, an ordinary white T-shirt has a UPF of 5, so it allows 1/5 (or 20 percent), of the sun’s UV radiation to reach the skin.

The UPF rating system was developed in 1994; In the USA, the American Association of Textile Chemists and Colorists (AATCC) Text Method 183 sets the standard for UPF testing. The ASTM D6544 plays a role in making sure UPF garments retain their sun protection properties throughout the life of the garment.

UPF clothing works to protect your skin by converting UV energy to heat, making it harmless. It does this by blocking or absorbing the UV rays.

• Clothing with a UPF designation on its label has been tested and deemed to protect its wearer from UVA and UVB radiation, as long as it has a rating of 15 or higher; in some cases, it may also have been treated with colorless dyes or chemical UV absorbers that block both UVA and UVB rays. The UPF rating is based on a fabric’s content, weight, color, and construction. But a fabric does not have to be labeled as such to provide UV protection.

UV radiation can damage your skin in as few as 15 minutes, so wearing clothing to protect yourself should always be your number-one priority when out in the sun. Prolonged exposure to UV radiation has dramatic health effects on the skin, the eyes, and the immune system:

• The most immediately visible expression of these is sunburn (erythema), followed by premature aging (photoaging) with repeated exposure to the sun—damage that adds up over your lifetime.
• The most serious consequence is skin cancer, with 66,000 deaths worldwide attributed annually to melanoma and other skin cancers.
• Additionally, prolonged sun exposure has been linked to cataracts, the clouding of the lens of the eye that can lead to blindness.

Children are an especially vulnerable population: the Centers for Disease Control reports that a few serious sunburns obtained during childhood increase a child’s risk for developing skin cancer later in life.

There is wide agreement among dermatologists that UPF clothing works, and actually delivers more effective protection from the sun, and more reliably, than other means. But the amount of coverage is key, and the more skin you cover, the better protection you can expect: a long-sleeved shirt is better than a short-sleeved one, and pants are better than shorts.

Fair-skinned people stand to benefit the most from UPF clothing, but any skin type will benefit from it at least some. Ratings are scaled as follows:

• 15 to 24—Good
• 25 to 39—Very Good
• 40 to 50—Excellent

It’s best to choose clothing with a UPF rating of 30 or higher; UPF 50 blocks 98 percent of UV radiation. And unlike sunscreen, UPF clothing works indefinitely—there is nothing to reapply for continued protection.

All clothing protects your skin from harmful UV radiation to some extent, and clothing is generally the best means of protection. Beyond clothing that bears a specific UPF label, look for these benchmarks.

Material Synthetics top the list for protection from UV radiation. Nylon offers highly effective protection, and both wool and silk are moderately effective. Cotton, rayon, flax, and hemp are less effective unless they have been chemically treated. The most protective cotton is unbleached or naturally colored. But untreated denim can provide superior protection, with a UPF value of 1700, meaning only 1/1700th of the sun’s ultraviolet radiation penetrates it.

• Colors that absorb UV radiation help reduce exposure to it. Dark colors are effective, but reds and other brights can absorb UV rays, too—the more vivid the color, the better it protects. Lighter colors can block UV radiation if the material’s weave is tight enough or it is chemically treated.
• High concentrations of premium dyes are used in some UPF-labeled clothing; typically, the higher the concentration of the dyes, the darker the material. Also, look to pigment-dyed fabrics for UV protection—these are textiles colored with a process that chemically binds the color to the material’s fibers.
• Tighter weaves are usually better UV blockers. You can get some idea of the effectiveness of a garment’s weave by holding it up to the light, but weave should not be the only yardstick to measure a textile’s UPF properties: the human eye can detect light, but it can’t see ultraviolet rays—even a tight weave can be breached by UV radiation.
• Keep it dry: While wet fabric can lose up to 50 percent of its UPF effectiveness for reasons not completely known, Orvis offers a selection of UPF clothing that retain UPF 50+ even when wet, including DriCast™ and Orvis PRO Sun. Faded fabrics are also less effective UV barriers. Choose quick-drying clothing for fun in the sun.

Choosing a garment with a UPF label ultimately takes the guesswork out of measuring whether it effectively blocks or absorbs UV rays, as its material will have been tested in a laboratory. And UPF-labeled garments now come in a wide range of colors and weights.

Quick Tips:

Wash natural fiber clothing several times to maximize shrinkage of the “holes” in the weave.

• Weight—The heavier the better when it comes to UV protection. And while you may not consider this ideal if you are bound for the beach, ventilation holes are added to some UPF clothing for improved air circulation and comfort.
• Elasticity—Stretchy clothing provides less protection than clothing without stretch because the weave expands when the material stretches. The correct fit is especially important in stretch clothing.

Wash your clothing with a UPF detergent additive or an optical brightening agent, which will enhance its natural UPF properties.