Mammillaria

Summary (1) A full description is given of mammillaria, the characteristic change in the skin which follows severe or moderately severe prickly heat in a humid climate. In a dry climate it is possible that the change does not occur. (2) Mammillaria is often associated with alterations in the quantity of sweating. Over the affected areas sweating may be reduced while elsewhere it may be increased. (3) Mammillaria itself is symptomless apart from a feeling of warmth and “fullness” under the skin on exposure to heat stress. However, the associated reduction in sweating may lead to other symptoms. (4) Mammillaria appears to be an invariable feature of anhidrotic heat exhaustion in humid climates, probably because severe prickly heat is a common antecedent factor in both conditions. In a hotter and drier climate, just as prickly heat is apparently often not succeeded by mammillaria, so anhidrotic heat exhaustion often occurs without this skin change. (5) The anatomical basis of mammillaria is discussed and it is concluded that the skin change cannot be due to obstruction of the sweat ducts. (6) An appearance similar to mammillaria has been noted in a few individuals who have never been in a tropical climate.