(Lichen tropicus; Prickly heat; Sweat eczema; Miliaria rubra)
Definition. An acute obstructive disorder of the sweat-glands, papulovesicular in character, with redness and itching.
Symptoms. Miliaria is a disease of hot weather and usually attacks the stout or those too warmly clad and hence inclined to sweat freely. The eruption appears in the form of pin-point to pin-head-sized, acuminate, bright red papules, often capped with tiny vesicles or pustules, which appear suddenly and in great numbers, situated commonly on the chest, neck, back, abdomen or arms, rarely on the face or other regions. They are discrete but closely crowded together and often there is more or less erythema. Sometimes the papules predominate (miliaria papulosa). The variety of miliaria called lichen tropicus or prickly heat is apt to be more popular in character. Nearly always, however, the vesicles are in much greater proportion (miliaria vesiculosa). After a few days the vesicles become opaque (miliaria alba). The sweat rash (red gum or strophulus) of infants is a form of miliaria due to overdressing, and in the very young often occurs on the side or part which rests against the mother during nursing. The vesicles of miliaria do not rupture spontaneously, hence there is no weeping of the surface; if torn by scratching, a crust forms and is shed in a few days. Pricking and itching sensations are often severe and anything which stimulates the circulation or promotes sweating aggravates the pruritus. A few cases of chronic miliaria have been reported by English observers but it is extremely rare. So-called miliary fever, a rare and epidemic disease, has not appeared in recent years, hence it is futile to discuss the condition from a historical standpoint only.
Etiology and Pathology. Profuse sweating as the results of hot weather, obesity, faulty clothing, local filth, too free use of stimulating foods or drinks, absorption of toxic products from intestinal disorders or irritating properties of the sweat itself have all been noted as causal factors. There is a growing opinion that vasomotor disturbances are not infrequently causal. Microscopically, minute sweat-cysts may be found in the epidermis caused by obstruction of the sweat-glands or by epidermal inflammation due to the irritating quality of the surface sweat.
Diagnosis. The association of miliaria with sweating during the warm weather and the absence of constitutional symptoms will generally suffice to distinguish it from the eruption of other diseases. In vesicular eczema the vesicles rupture and there is oozing and crusting, with a tendency to persist; whereas, miliary vesicles do not rupture and the individual eruption is transitory. The occasional association of miliaria with the cutaneous manifestations of infectious diseases is to be borne in mind in suspicious cases. It may so closely resemble the exanthemata, especially scarlet fever, as to call for careful differentiation of constitutional symptoms.
Prognosis and Treatment. The duration is about a week for a single outbreak but during a hot spell, fresh crops are likely to prolong the attack. The general health is unaffected unless secondary infection ensues, and a change of air or cooler weather usually mitigates the attack at once. Prophylactic treatment is most important in preventing recurrence. In this particular, the diet, clothing and bathing of children may need attention, and constipation and gastrointestinal disorders should be investigated. Lactobacillin has done veoman work along this line. Externally, mild sedative or cooling lotions or dusting powders will suffice. Saturated solution of boric acid, or 10 per cent. hamamelis with or without alcohol may be tried for localized forms, while bran, starch or alkaline baths will help extensive involvement. Am mur., Antim crud., Belladonna, Bryonia, Jaborandi, Hydrocot. and Sulphur may be studied.