An extreme fear or avoidance of sunlight and bright conditions, occurring in some organisms or psychological disorders.
From Greek helios (sun) + -phobia (fear of, from phobos). This medical/biological term follows the standard -phobia pattern for naming fears that became systematic in medicine during the 19th century.
Some people with severe photosensitive conditions like severe lupus or porphyria develop heliophobia—their bodies literally react dangerously to sunlight, creating a real psychological aversion that's grounded in actual medical threat!
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