What SPF Doesn't Tell You: Reading UVA Protection After a Peel

An SPF number describes UVB protection only. It says nothing about UVA , the part of the spectrum that reaches the dermis, degrades collagen and elastin, and drives the pigmentation and photoageing that undo resurfacing work. It is the half of the picture the number on the tube leaves out entirely.

That single fact accounts for most of the confusion around sun protection, including among clients who consider themselves careful about it. A high number feels like complete protection. It isn't a measure of completeness at all.

Three things are worth knowing, and worth passing on at the end of a treatment.

SPF and UVA are measured separately

SPF is a ratio: the UVB dose that produces minimal erythema on protected skin, divided by the dose that produces it on unprotected skin. Erythema is a UVB response, so that is what the number tracks.

UVA protection is assessed by separate methods and reported separately. A product that protects against both will say so, through a UVA marking, a stated UVA filter, or a broad-spectrum claim, whereas an SPF figure on its own confirms one half of the picture.

The practical consequence: a higher SPF extends UVB protection and tells you nothing new about UVA. Moving a client from SPF 30 to SPF 50 is not automatically an improvement in the protection that matters most after a peel.

The number on the tube isn't the protection achieved

SPF is tested at 2 mg/cm² of product, around a third of a teaspoon for a face. Almost nobody applies that much in practice, and using less doesn't reduce protection proportionally: it falls away faster than that. A client applying an SPF 50 sparingly is not getting SPF 50.

Reapplication follows the same logic. At least every 2 hours during exposure, and immediately after swimming, sweating or towel-drying, whatever the number on the tube. A high SPF buys longer UVB protection; it doesn't remove the need to reapply, and it doesn't survive being towelled off.

What to say at the end of a treatment session

Skin leaving a peel is at its most photosensitive, and a client's habits over the following days decide whether the result holds or pigmentation arrives to replace it. Worth stating plainly, because none of it is obvious from packaging:

• Use more product than feels necessary, the tested amount is more than most people apply.
• Reapply at least every 2 hours during exposure, and after swimming or towelling.
• Check the product covers UVA as well as UVB, rather than reading the SPF figure alone.
• Apply on overcast days too, UV reaches the skin through cloud.

Ekseption's All-Day Shield (SPF 50), All-Day Shield Fluid (SPF 25) and All-Day Shield Serum (SPF 15) contain both UVA and UVB filters alongside red algae extract and ferulic acid, and are formulated for use on skin that has been peeled. Each product page lists its full performance figures.