DERMATOLOGY

The skin is subjected, more than any other tissue, to external, physical, chemical and bacteriological attacks. It responds to it by nonspecific vascular and tissue reactions, sometimes following an allergic mechanism. Secondly, the skin is often the seat of manifestations which depend on internal disorders, of an infectious, metabolic or immunological order; these skin symptoms are often the revealing signs of the general disease in question (cf. MEASLES). Finally, the various tissues of the skin (epithelial, connective, pigmentary system) can proliferate, either by disorders of embryogenesis (congenital cutaneous dystrophies, nevi, angiomas), or by the action of known or unknown acquired factors (malignant tumors and reticulopathies). The field of dermatology is too vast for it to be possible here to review all the affections of the skin. The syphilis and leprosy , skin essentially in translation, as well as tuberculosis and vascular and blood disorders, are studied in other articles (hematology, leprosy, syphilis, tuberculosis).

A biopsy is so easy to perform on the skin that it constitutes an almost clinical act: patients should not interpret this recourse to histological examinations as the index of a malignant disease.

Skin lesions caused by exogenous factors

Physical factors

Mechanical and physical agents determine wounds and traumatic ulcerations , accidental or provoked (pathomimia), burns , frostbite (frostbite), lucites and post-therapeutic and occupational radiodermatitis.

Natural (sun) or artificial light rays (tanning lamps, phototherapy), especially ultraviolet B rays (290-320 nm), determine skin reactions of phototoxicity or photoallergy.

JUVENILE ACNE

On oily skin , known as seborrheic, juvenile acne, or polymorphic acne, occurs in both sexes at puberty.

The starting point is the comedo. Black comedones, a mixture of keratin and sebum, obstruct the orifice of pilosebaceous follicles; keratin or dust color them black. They can be easily extracted with the help of suitable devices. White comedones, true microcysts obstructing follicular canals, resist any attempt at extirpation by pressure. It is mainly from them that suppurative formations develop: pustulettes with the pilosebaceous orifice and in depth small abscesses or larger inflammatory tuberosities, or even true boils. The association of these various elements produces a polymorphic eruption, and depending on the predominance of one of them, comedonal, papular, tuberous acne is described.

Acne sits in the areas of choice for seborrhea . The face, forehead, nasolabial region and chin are especially affected. Elsewhere, the interscapulo-vertebral and prethoracic, sometimes deltoid, areas are affected.

Beginning at puberty, acne progresses by outbreaks, at the origin of which we evoke intestinal disorders, excess absorption of sweets or fat and, more clearly, a premenstrual upsurge.

While it is common to see acne subside around twenty – twenty-five years, this evolution is not constant, and revisions are possible.

In addition, if it has not been treated, acne leaves indelible scars, sometimes very significant, so called “worming”. These scars are favored by the manipulations that some make undergo to their “buttons” and in particular by the digital expression.

Generally considered to be benign, acne, which is highly unsightly, can cause mental disorders, and in particular in excoriated acne in young girls, or on occasion

ACNE ROSACEA

Mostly in women around menopause, but sometimes in both sexes and at any age, acne rosacea can start on dry skin . It is preceded by a stage of facial erythrosis occurring at the beginning intermittently, on the occasion of sudden changes in temperature, absorption of alcoholic beverages, a too abundant meal in the premenstrual period or following various disturbances of psychological order. The flushing becomes more and more frequent and the erythrosis becomes permanent. At the same time, fine telangiectasias appear, first limited to the cheekbones and then more and more extensive. Conjunctivitis is frequently associated with these skin changes.and papulo-pustules which can occur in sudden outbreaks, disfiguring patients. The course is indefinite in the absence of treatment.

In other cases, acne rosacea develops on oily skin, at any age, in subjects who have generally presented with juvenile acne , often male, sometimes deforming the appearance of the nose (rhinophyma). Many etiological factors have been mentioned: digestive and circulatory disorders in particular, neurovegetative imbalance, various allergies, in particular to Candida albicans , role of emotions.

One particular variety is symptomatic of ariboflavinosis. It is accompanied by the formation of more or less thick crusts and ocular involvement detected by ophthalmological examination.

The local treatment of acne rosacea at the best skin specialist in south delhi is very delicate, because the integument of these subjects is particularly sensitive and intolerant. Water, soap and sulfur are often poorly tolerated. Local treatment calls for benzoyl peroxide (or metronidazole), combined with general antibiotic treatment in small doses, the mechanism of action of which remains obscure. Fine electrocoagulation of telangiectasias, and above all aetiologic treatment, when precise indications are available, allow most patients to be cured.

ALLERGY & HYPERSENSITIVITY

The notion of allergy relates to the paradoxical phenomenon of the harmfulness of certain immune reactions. The authorship of this concept (which appeared in 1906) goes to the Viennese doctor Clemens von Pirquet. He sought in particular to explain by this “altered reactivity” (translation of the Greek terms united in the word allergy) the hazards of immunotherapy, then in its infancy.

In Paris, Émile Roux , a disciple of Louis Pasteur , had succeeded, in 1894, in vaccinating horses against the diphtheria bacillus, in order to be able to extract from their blood an anti-diphtheria serum containing defensive substances acting against this microbe in the subjects he infected.

However, the reliability of this serotherapy had to be evaluated beforehand in order to ensure the success of the treatment. It was Paul Ehrlich who, at the Institute for the evaluation of sera, in Frankfurt, established a few years later the principles making it possible to measure the effectiveness of the defense reaction provided by “antibodies” of the serum – specifically protective. – with regard to microbial “antigens”.

It therefore became possible to avoid the hazards of serotherapy. Nevertheless, it was found that everything was not settled: accidents (serum sickness) remained unpredictable. The responsiveness of the people treated therefore remained an essential element of therapeutic success. But Charles Richet and Paul Portier had already shown from the beginning of the XX ^th  century, non-responsiveness could have lethal effects (anaphylaxis phenomenon or “inadequate response”).

It was therefore essential that research in allergy, that is to say, on alterations in reactivity were associated with the development of vaccines and sera that was to mark the first half of the XX ^th  century. They have invested in particular a whole panoply of hypersensitivity reactions affecting certain subjects put in