A gelotologist specialises in gelotology, the study of humour, laughter and the exercising of the gelastic muscles, a deeply serious exploration of what happens to our bodies’ physical systems, such as respiration and circulation, when we’re exposed to humour.
The topic is as yet relatively specialised, though the word gelotology can be traced back at least as far as a widely syndicated report in US newspapers around April 1971 about the San Francisco Gelotology Institute. Its director, Dr William F Fry Jr, argued — in total opposition to current thinking — that laughter is actually very bad for you, because it increases the heart rate, interrupts normal breathing, and may contribute to hernias and ulcers.
The word comes from Greek gelos, laughter. It’s a close relative of the adjective gelastic, either something funny or a remedy that works by making us laugh, no doubt on the principle of laughter being the best medicine (a gelotherapist builds on this idea by specialising in what is sometimes called laughter therapy). However, a gelastic seizure is a form of epilepsy that causes the sufferer to laugh. Geloscopy, an excessively rare word, is divination by means of laughter.
An alternative spelling not infrequently seen is gelatologist. You may feel this would better refer to a maker of Italian ice creams, or possibly some arcane culinary specialist in the use of gelatine.