Photolyase

Photolyase is a DNA repair enzyme, usually derived from algae or cyanobacteria and listed on ingredient lists as plankton extract. It belongs to the same small category as micrococcus lysate, and works by a genuinely different mechanism.

The damage it repairs

UVB radiation causes adjacent pyrimidine bases in a DNA strand to bond to each other, forming cyclobutane pyrimidine dimers. These distort the helix and interfere with replication. Accumulated unrepaired dimers are central to both photoageing and skin cancer.

How photolyase differs

This is the interesting part. Most DNA repair works by excision: the damaged section is cut out and rebuilt. That is how human nucleotide excision repair operates, and how micrococcus lysate's UV endonuclease initiates repair.

Photolyase does something else. It binds the dimer and uses energy from visible blue light to directly break the bond, restoring the two bases to their original state. No cutting, no rebuilding.

This is called photoreactivation, and it requires light to work. Photolyase without exposure to visible light does nothing.

Humans do not have it

Placental mammals, including humans, lost functional photolyase during evolution. Most other organisms retain it, including bacteria, plants, fungi and marsupials.

So a topical photolyase is not supplementing an existing human mechanism. It is supplying one that human skin does not possess at all, which is a more unusual proposition than most cosmetic ingredients make.

What that means practically

A product containing photolyase is designed to be used where visible light will reach it. Applying it and then sitting in the dark defeats the mechanism.

This has led some formulators to position photolyase products for daytime use under sunscreen, on the reasoning that visible light passes through most sunscreens while UV does not.

The evidence

Studies using liposomal photolyase have reported reduced measurable dimer formation after UV exposure, including work in people with xeroderma pigmentosum, a genetic condition in which repair capacity is absent. That research is real and reasonably compelling as biology.

The cosmetic question is different. Photolyase is a large protein, the barrier excludes proteins, and the target is inside the cell nucleus. Whether any given product delivers intact enzyme to where it would act depends entirely on formulation, and the ingredient list will not tell you.

The label problem

"Plankton extract" is the INCI name, and it is uninformative. It tells you the material came from plankton. It does not confirm photolyase is present, in what quantity, or in what state.

Some formulations name it more specifically or state the enzyme content. Most do not.

Alongside micrococcus lysate

The two are frequently combined, since they address the same lesions by different routes: photolyase reverses the bond directly, endonuclease initiates excision repair. Products aiming at DNA repair often include several enzymes for that reason.

The honest position

None of this substitutes for sun protection. Preventing damage remains considerably more reliable than repairing it, and every serious discussion of DNA repair enzymes in skincare says so.