St. Tropez Sign
Authors: Sophie Ramos, Alvin Leung
Chief Editor: Dr Daniel Keith
The St Tropez sign is seen on dermoscopy when a skin lesion (most commonly a seborrheic keratosis) is stained with tanning product.
Macroscopic Appearance
The macroscopic appearance is of a dark seborrheic keratosis (see more on seborrheic keratosis page). Fake tan accumulates in the cracks on the surface of the lesion and can be retained for months after use of the tanning product – even after the fake tan has washed off the surrounding skin!
This is becoming more common as public awareness of the dangers of UV radiation is causing a switch to artificial tanning.
Patients typically complain of a change in colour of a pre-existing mole - with no change in size, shape or texture. (This is when having a photograph of the pre-existing lesion becomes particularly helpful!)
Macroscopic appearance of a seborrheic keratosis on Fitzpatrick skin type II.
It is important to note the patient explained this mole was previously “white” before using sun cream with tanning product in it.
Less commonly, the St Tropez sign can also be seen on compound naevi. Similar to seborrheic keratosis, compound naevi often have uneven surfaces, making it easier for fake tan to lodge and form deposits.
Other than accumulating in cracks, fake tan containing dihydroxyacetone (DHA) has alsobeen found to react more with thickened, hyperkeratotic skin, forming melanoidin and leaving pigmentation behind. This explains how fake tan may darken both the fissures aswell as the raised parts of lesions.
Macroscopic appearance of a compound naevus on Fitzpatrick skin type I.
It is worth noting that the colour of the compound naevus is distinctively different from the nearby naevi.
Note: Using an isopropyl alcohol swab to clean the lesion will eliminate the St. Tropez sign, restoring the skin/lesion to its original appearance.
Dermoscopic Appearance
Unannotated example of the St Tropez sign in a seborrheic keratosis under dermoscopy.
Annotated and zoomed in example of St Tropez sign in a seborrheic keratosis, showing circular deposits of exogenous pigment in hyperkaratotic areas.
A network of varying pigment can be seen, forming a lobular pattern. There is no remaining pigmentation on the surrounding skin.
Unannotated example of St Tropez sign on a compound mole under dermoscopy.
Annotated example of St Tropez sign on a compound mole under dermoscopy.
Deposits of exogenous pigment in hyperkaratotic areas form a dark brown speckled appearance. The rest of the lesion has a lighter, reddish colouration, suggesting fake tan-induced pigmentation to a lesser extent.
Unannotated example of St Tropez sign on a compound mole under dermoscopy.
Annotated example of St Tropez sign on a compound mole under dermoscopy.
Deposits of exogenous pigment in hyperkaratotic areas form a dark brown streaked appearance.