Solar Lentigoes, Cryotherapy & Post-Inflammatory Pigmentation

London Dermatology | 1 August 2024

Tannability and burnability are two characteristics that are separately inherited. lannability from one ancestor may seduce and tempt you to tan but, if you have also inherited burnability from another ancestor, each time you tan you will also burn and will, in due course, develop brown spots.

Solar lentigoes (i.e. brown spots) develop in people who have inherited burnability. They are the result of sun exposure 20 or so years earlier. Once solar lentigoes appear, they increase in size and darken in colour with each successive year. They can usually be improved by cryotherapy (i.e. freezing with nitrogen spray). To try to get an optimal result, cryotherapy treatment is performed over three sessions. This improves the chance that most of the brown solar lentigoes will clear completely and lessens the chance that they will be replaced by white marks. Some test areas of cryotherapy are sometimes performed on a few brown spots prior to the first full treatment session.

In people with tannable skin, any injuries to the skin, for example an oven burn on the wrist or a cryotherapy treatment, may be followed by the temporary appearance of a dark mark. This temporary pigmentation phenomenon is called post-inflammatory hyperpigmentation (PIH). It is less likely to occur if the treated areas are protected from sun for a few weeks after each cryotherapy treatment. If PIH does occur, untreated it may last on face and neck up to about five months, on the chest up to about eleven months and on the back or thighs up to 18 months. PIH, if it occurs, resolves on its own without any treatment. Its resolution rate can be hastened by the use of a depigmenting cream. In patients with a tannable complexion, there is always a risk of PIH and, to try to minimise that risk, each freezing session needs to be gentle. This means that in patients who are susceptible to PIH, sometimes more than three treatment sessions are needed to clear solar lentigoes.

There is a balance here between the desire to try to clear the solar lentigoes rapidly and the wish to try to avoid PIH.

Since brown spots are permanent and set to darken and grow larger over the ensuing years, whereas PIH is temporary, for most patients the benefit from removing the permanent brown spots outweighs the inconvenience of the risk of temporary PIH.