Skin & Hair · Involuntary responseGoosebumps
Raised hair follicles in response to cold or emotion.
Frequency: CommonInvoluntary response
Skin & Hair · Involuntary response
Brain · Involuntary responseAn earworm
A short passage of melody continues internally without a conscious decision.
Frequency: Common
Skin & Hair · Involuntary responseWrinkled fingers in water
Finger skin wrinkles after prolonged contact with water.
Frequency: Common
Skin & Hair · Involuntary responseDermatographism
Light scratching pressure produces temporary raised lines.
Frequency: Varies by individual
Skin & Hair · Involuntary responseBlushing
Feeling observed or embarrassed can suddenly redden the face.
Frequency: Common
Nerves · Involuntary responseAwake but unable to move
When falling asleep or waking, REM-related muscle inhibition briefly persists despite awareness.
Frequency: Varies by individual
Nose · Involuntary responseNasal cycle
The nasal turbinates alternate rhythmically between greater and lesser blood flow.
Frequency: Common
Mouth & Throat · Involuntary responseGustatory sweating
The face or head sweats while eating.
Frequency: Varies by individual
Heart & Circulation · Involuntary responseRespiratory sinus arrhythmia
The pulse becomes slightly faster when inhaling and slower when exhaling.
Frequency: Common
Nerves · Involuntary responseThe REM muscle brake
During REM sleep, a brainstem network suppresses skeletal muscles and usually prevents acting out dreams.
Frequency: Common
Nose · Involuntary responseSide sleeping and a blocked nose
When lying on one side, the lower nasal side often swells more.
Frequency: Common
Muscles · Involuntary responseMuscle tremor after exertion
Fine involuntary oscillations during or after muscle exertion.
Frequency: Common
Nerves · Involuntary responseDreams become physical
In a rare disorder, normal REM atonia is partly absent, so dreams can be acted out with movement.
Frequency: Rare
Heart & Circulation · Involuntary responseVasovagal reaction
Pain, seeing blood, or prolonged standing can trigger nausea, warmth, and near-fainting.
Frequency: Varies by individual
Muscles · Involuntary responseEyelid twitching
Fine, involuntary twitching of an eyelid.
Frequency: Common
Nerves · Involuntary responseYawning
Yawning is an involuntary sequence of inhalation, mouth opening, and stretching.
Frequency: Common
Nose · Involuntary responseSneezing after eating
Some people sneeze after a large meal.
Frequency: Frequency unclear
Internal Organs · Involuntary responseBeetroot in urine
Beetroot can color urine pink to red.
Frequency: Varies by individual
Muscles · Involuntary responseFasciculations
Visible twitching of small muscle bundles beneath the skin.
Frequency: Common
Nose · Involuntary responseNosebleed in dry air
Dry mucosa can make small vessels more likely to rupture.
Frequency: Varies by individual
Muscles · Involuntary responseMuscle cramp
Sudden painful involuntary muscle contraction.
Frequency: Common
Internal Organs · Involuntary responseLactose intolerance
Undigested lactose can cause gas and diarrhea.
Frequency: Varies by individual
Mouth & Throat · Involuntary responseInvoluntary tongue movements
Rare involuntary tongue movements can interfere with speech and swallowing. Causes range from medications to movement disorders.
Frequency: Rare
Internal Organs · Involuntary responseGallbladder contraction after a meal
Fatty food triggers emptying of the gallbladder. This usually goes unnoticed.
Frequency: Common
Internal Organs · Involuntary responseMigrating motor complex
Between meals, the stomach and small intestine pass through recurring phases of movement.
Frequency: Common
Brain · Involuntary responseSleepwalking
During sleepwalking, a person performs complex movements while only partly awake.
Frequency: Varies by individual
Nerves · Involuntary responseItch-scratch reflex
Scratching can briefly suppress an itch, but excessive scratching increases skin irritation.
Frequency: Common
Eyes · Involuntary responseGustatory lacrimation
Rarely, the eyes water during chewing or eating.
Frequency: Rare
Ears · Involuntary responseExploding head syndrome
While falling asleep or waking, a person may experience a sudden loud noise with no external source.
Frequency: Frequency unclear
Brain · Involuntary responseContagious yawning
Seeing or hearing a yawn can cause some people to yawn themselves.
Frequency: Varies by individual
Internal Organs · Involuntary responseCoffee-induced bowel movement
Coffee can increase the urge to have a bowel movement in some people.
Frequency: Varies by individual
Nerves · Involuntary responseTransient pressure-related paresthesia
After sitting awkwardly, a foot may become numb and then tingle when pressure is released because its nerves were temporarily impaired.
Frequency: Common
Mouth & Throat · Involuntary responseMorning breath
Breath often smells stronger after sleep.
Frequency: Common
Internal Organs · Involuntary responsePost-micturition dribble
A few drops may emerge from the urethra after using the toilet.
Frequency: Varies by individual
Skin & Hair · Involuntary responseCold hands
Hands can feel especially cold in low temperatures or during stress.
Frequency: Common
Mouth & Throat · Involuntary responseBlack hairy tongue
Elongated tongue papillae can form a dark, hair-like coating.
Frequency: Frequency unclear
Skin & Hair · Involuntary responseCold-induced cyanosis
Nail beds may temporarily look bluish in the cold.
Frequency: Frequency unclear
Skin & Hair · Involuntary responsePalmar hyperhidrosis
Excessive sweating of the palms, often during stress or heat.
Frequency: Varies by individual
Mouth & Throat · Involuntary responseSwallowing during sleep
Saliva and secretions are swallowed even during sleep.
Frequency: Common
Mouth & Throat · Involuntary responseBruxism
Jaw muscles clench or grind the teeth, often at night.
Frequency: Varies by individual
Mouth & Throat · Involuntary responseNausea salivation
The mouth can suddenly become watery before vomiting.
Frequency: Varies by individualSurprisingly quiet here.
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