Psychologists call squeamishness ‘disgust sensitivity’ or ‘disgust proneness’. Disgust is an evolved emotional reaction that prompts us to avoid potentially contaminating material, such as blood, pus or faeces. This has obvious survival advantages, helping us to avoid infectious diseases and toxic food, but an overly sensitive disgust response can have drawbacks – making us less likely to try new foods, for instance, or board a crowded train.
The survival value of different levels of squeamishness will have varied depending on the circumstances our ancestors found themselves in, and variability in the emotion has been passed down through the generations. Our disgust sensitivity is also influenced by early social learning, such as from our parents’ disgust reactions, and by cultural customs around hygiene and purity.