Trypophobia is an aversion to the sight of irregular patterns or clusters of small holes, or bumps. It is not officially recognized as a mental disorder, but may fall under the broad category of specific phobia if fear is involved and the fear is excessive and distressing. People may express only disgust or both fear and disgust to trypophobic imagery. The understanding of trypophobia is limited. Although few studies have been done on trypophobia, researchers hypothesize that it is the result of a biological revulsion that associates trypophobic shapes with danger or disease, and may therefore have an evolutionary basis. Exposure therapy, which has been used to treat phobias, has been proposed as a treatment. The term trypophobia is believed to have been coined by a participant in an online forum in 2005. It has since become a popular topic on social media. Trypophobia is not recognized by name as a mental disorder, and so is not a specific diagnosis in the American Psychiatric Association's Diagnostic and Statistical Manual, Fifth Edition (DSM-5). However, it may fall under the broad category of specific phobia if the fear is excessive, persistent, and associated with significant distress or impairment. Whether trypophobia can be accurately described as a specific phobia might depend on whether the person mainly responds with fear or with disgust. Because phobias involve fear, a response to trypophobic imagery that is based mostly or solely on disgust renders its status as a specific phobia questionable. In one study, most of the participants with trypophobia met the DSM-5 criteria for specific phobia, even though they experienced disgust instead of fear when shown imagery of clusters of holes; however, they did not meet the distress or impairment criterion. Trypophobia often presents with an autonomic nervous system response. Shapes that elicit a trypophobic reaction include clustered holes in innocuous contexts, such as fruit and bubbles, and in contexts associated with danger, such as holes made by insects and holes in wounds and diseased tissue such as those caused by mango worms in animals, especially dogs. Upon seeing these shapes, some people said they shuddered, felt their skin crawl, experienced panic attacks, sweated, palpitated, or felt nauseated or itchy. Other reported symptoms include goose bumps, body shakes, feeling uncomfortable, and visual discomfort such as eyestrain, distortions, or illusions. Trypophobia may manifest as a reaction of fear, disgust, or both. Disgust is usually the stronger emotion in those with trypophobia. The understanding of trypophobia is limited. Several possible causes have been proposed. Geoff Cole and Arnold Wilkins believe the reaction is an 'unconscious reflex reaction' based on a biological revulsion, rather than a learned cultural fear. Imagery of various venomous animals (for example, certain types of snakes, insects, and spiders) have visual characteristics similar to trypophobic imagery. Because of this, it is hypothesized that trypophobia has an evolutionary basis meant to alert humans of dangerous organisms. Can et al., however, believe the connection between trypophobia and evolution as a result of a threat from deadly creatures to be weak and that, if it does exist, it manifests later in life.