A Psoriasis affects about two per cent of the population at some time. It is most common in those aged 10 to 30 years old, so your daughter falls within the usual bracket.

However, since people in their teens and 20s tend to be self-conscious about their looks, psoriasis is all the more distressing on the face at that age - even without the physical discomfort it can often cause.

Most conventional treatments of psoriasis are aimed at improving symptoms rather than getting to the root of the problem. However, they come with a raft of risks, limitations and side-effects, so you may find it helpful to be forearmed with the facts.

Topical steroids are recommended where, as in your daughter’s case, the psoriasis covers 5 per cent or less of the body. They can take effect quickly, but come with a range of side-effects such as thinning of the skin, which can make the symptoms worse.

Tar creams, another commonly prescribed topical preparation, have fewer side-effects, but can take up to 12 weeks to work and are messy to apply.

Vitamin derivatives are based on vitamins A or D, but are not, as they may sound, naturally based substances. They often cause skin irritation and can only be used for a maximum of 12 weeks.

Systemic drugs are generally only prescribed for severe psoriasis. Cyclosporin, methotrexate, acitretin and hydroxyurea are the most widely used, but can cause hypertension, kidney damage, anaemia and reduced immunity. However, your daughter’s case sounds mild-to-moderate, it is unlikely to merit such a powerful treatment regime.

Biological drugs seek to stem the development of psoriasis by targetting the immune system as psoriasis is considered an autoimmune condition. These drugs seek out dysfunctional immune T cells, or the chemical messengers they release, to eliminate the psoriatic process at source.

However, these novel agents do have drawbacks: they need to be taken by injection; they are expensive; they must be used continuously to maintain any improvement; and perhaps most important of all, their long-term safety is still under evaluation.

The good news is that there’s a wide range of alternative treatments available. So, before taking your daughter out of school, it’s worth trying out some of the alternatives that have proved effective for mild-to-moderate psoriasis. But first, it helps to understand what’s caused it.

The rough, raw skin that characterises psoriasis is due to accelerated skin-cell division. These cells replicate more rapidly than the body is able to shed them - in acute cases, at 1000 times the usual rate - so they build up on the skin surface.

The problem originates not in the skin itself, but in the immune or digestive system. Irritable bowel syndrome, ulcerative colitis or Crohn’s could be the source of the problem, so check these out first.

In the case of immune dysfunction, skin cells super-generate and, as they migrate towards the skin surface, they act as if they are fighting an infection or healing a wound, hence, the resulting inflammation. The role of immunity explains why psoriasis often starts or flares after an infection such as a sore throat.

Assuming you have discarded the possibility of a gut problem, a sensible two-pronged approach would be to target both the immune system, where it starts, and the epidermis, where it surfaces.