😢 Why Do We Cry?

What you’ll learn

1. Three kinds of tearsDistinguish the three types of tears (basal, reflex, emotional) and understand that they differ in both trigger and chemical composition.Your eyes make three different tears: basal tears that constantly lubricate, reflex tears that flush out irritants, and emotional tears tied to feeling. They flow from the same glands but answer to different signals. Emotional tears appear to carry higher levels of substances like ACTH, prolactin, and the painkiller leucine-enkephalin, though these are small studies whose meaning is still uncertain.
2. The lonely human cryExplain why humans appear unique in shedding emotional tears and describe the leading social-signaling theory for why emotional crying evolved.Humans seem to be the only animals that weep from emotion; others feel deeply but do not appear to shed emotional tears, likely due to distinctive brain wiring. A leading theory, associated with Ad Vingerhoets, is that tears are an honest social signal of vulnerability that draws comfort and support from others. This is presented as a theory, not settled fact.
3. What crying does to youDescribe what happens physiologically during a cry and critically evaluate the popular 'tears release stress/toxins' claim.During a cry the body tends to shift toward the calming parasympathetic state, which may explain the post-cry sense of relief, though whether you feel better depends heavily on context and support. The popular claim that crying flushes out stress hormones or toxins comes from William Frey's hypothesis, which has weak evidence. The tiny fluid volume and animal studies suggest any relief comes from the nervous system settling, not detoxification.
4. Why onions wreck youTrace the enzymatic chemistry of onion-induced tears and explain the eye-irritation mechanism that produces reflex tears.Cutting an onion ruptures cells and unleashes enzymes: alliinase makes unstable sulfenic acids, then lachrymatory factor synthase converts them into the volatile gas syn-propanethial-S-oxide. The gas drifts to your eyes and reacts with the moist tear film to form a trace of mild sulfuric acid. Your cornea's sensitive nerves detect it and trigger reflex tears to flush the irritant out.

Questions this course answers

Grounded in trusted sources

• Bylsma, Gracanin & Vingerhoets, 'The neurobiology of human crying' / 'Is crying a self-soothing behavior?' (Frontiers in Psychology, 2014) — PMC4035568
• Vingerhoets & Bylsma, 'The riddle of human emotional crying: a challenge for emotion researchers' and Gracanin et al., 'The social impact of emotional tears' (Motivation & Emotion, 2016)
• Library of Congress, 'Why does chopping an onion make you cry?' and ACS Molecule of the Week, 'syn-Propanethial-S-oxide'; Masamura et al., lachrymatory factor synthase structure (ACS Chem. Biol., 2017)

Every Wunder lesson is built from real, reputable sources — never invented.

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