question: Why do cold feet always sting when you enter a hot tub?
comment: Your skin is covered in temperature sensitive cells. They are what tells you that something is too hot or cold. But the way they do so is dependent on the temperature your body has been at recently. If it goes too far in either direction, these things start going off like alarms. The sudden change in temperature from cold to hot makes your body think you're touching something you shouldnt be, something too hot. The stinging / burning sensation is your body trying to make you stop doing that. Eventually though the cells establish a new base, safe temperature for the situation, and you stop feeling the stinging because it doesn't detect any problems. WHich is also why jumping into a cool pool immediately after a hot tub causes the same sensation. A semi-related bonus fact: this is the same reason why alcohol burns when you drink it. The alcohol confuses those temperature sensitive cells and reduces their threshold, so your own body heat is enough to set them off.
passages: Stings are most common in the hours before and after low tide (especially at springs), so one possible precaution is to avoid bathing or paddling at these times. Weever stings have been known to penetrate wet suit boots even through a rubber sole (if thin), and bathers and surfers should wear sandals, "jelly shoes", or wetsuit boots with relatively hard soles, and avoid sitting or "rolling" in the shallows. Stings also increase in frequency during the summer (to a maximum in August), but this is probably the result of the greater number of bathers.
   "Chironex fleckeri" is best known for its extremely powerful and occasionally fatal "sting". The sting can produce an excruciating pain accompanied by an intense burning sensation, like being branded with a red hot iron. In Australia, fatalities are most often caused by the larger specimens of "C. fleckeri".
   BULLET::::- Restriction of Blood Flow: Typing or other activities which tense muscles and reduce blood flow can cool the body parts enough to cause itching and hives.
  
  BULLET::::- Blood Flow: While putting hands or feet in hot water nails turn purple/white until the body gets used to the temperature.
  
  Section::::Diagnosis.
   A case of scorpion sting to the palm of the hand of a scuba diver occurred while trying on a wetsuit on the Osa Peninsula. Symptoms reported include localized pain for several hours with severity decreasing after the first hour. Localized tingling sensation was reported as well. Treatment several hours after envenomation with Therapik, a toxin-denaturing device utilizing heat, resulted in complete resolution of symptoms. (Feb 19,2016)
  
  Section::::Similar species.
   Section::::Distribution and habitat.
   Most human stings are inflicted by the lesser weever, which habitually remains buried in sandy areas of shallow water and is thus more likely to come into contact with bathers than other species (such as the greater weever, which prefers deeper water); stings from other species are generally limited to anglers and commercial fishermen. Even very shallow water (sometimes little more than damp sand) may harbour lesser weevers. The vast majority of injuries occur to the foot and are the result of stepping on buried fish; other common sites of injury are the hands and buttocks. 
   BULLET::::- Hot-tub folliculitis is caused by the bacterium "Pseudomonas aeruginosa". The folliculitis usually occurs after sitting in a hot tub that was not properly cleaned before use. Symptoms are found around the body parts that sit in the hot tub: the legs, hips, chest, buttocks, and surrounding areas. Symptoms are amplified around regions that were covered by wet clothing, such as bathing suits.
  
  BULLET::::- Sycosis vulgaris, Sycosis barbae or Barber's itch is a staphylococcus infection of the hair follicles in the bearded area of the face, usually the upper lip. Shaving aggravates the condition.
   Jerry and Jean-Paul oversleep but Jerry manages to get him to the race in time. At the race Jean-Paul manages to take the lead and is in first place as he nears the finish line. As he runs past Jerry, Kramer and Elaine he accidentally grabs a cup of hot tea from Kramer (who is still attempting to raise his core temperature) and is severely scalded by it after mistaking it for water, causing him to scream in pain and ultimately, fail to win the race.
   BULLET::::- Air Conditioning: Entering a cool building during a summer day can result in an allergic reaction to exposed areas of skin, congestion from breathing the cool air and possibly feeling fatigued.
  
  BULLET::::- Cold Foods/Drinks: Eating or drinking cold or cool substances such as ice cream or even iced tea may result in the individuals tongue and surrounding tissues swelling and to suffocation.
  
  BULLET::::- Cool/Cold Surfaces: Sitting on sidewalks which are cool, leaning on or grabbing a cold pole will result in hives forming on the area which had contact with the cool surfaces.
   Section::::Research findings.:Peripheral nervous system.
  
  Section::::Research findings.:Peripheral nervous system.:Receptors.
  
  Crayfish ("Procambarus clarkii") respond quickly and strongly to high temperatures, however, they show no response to low temperature stimuli, or, when stimulated with capsaicin or isothiocyanate (both are irritants to mammals). Noxious high temperatures are considered to be a potentially ecologically relevant noxious stimulus for crayfish that can be detected by sensory neurons, which may be specialized nociceptors.
   Stonefish stings are extremely painful and potentially lethal. The two most recommended treatments are the application of heat to the affected area, and antivenom. Hot water (at a temperature no higher than ) applied to the injured area has been found to denature stonefish venom, and causes minimal discomfort to the victim. Antivenom is used in more extreme cases. Vinegar is found on some Australian beaches as it is said to lessen the pain.
  
  Section::::Treatment of envenomation.:Stonefish stings in Australia.
   Section::::Venom.
  
  This species is responsible for up to 10,000 human stings in Australia each summer, particularly on the east coast, with some others occurring off the coast of South Australia and Western Australia. One of the problems with identifying these stings is that the detached tentacles may drift for days in the water, and the swimmer may not have any idea if they have been stung by a man o' war or by some other less venomous creature.
   BULLET::::- Itchy, burning skin. Irritant contact dermatitis tends to be more painful than itchy, while allergic contact dermatitis often itches.
  
  While either form of contact dermatitis can affect any part of the body, irritant contact dermatitis often affects the hands, which have been exposed by resting in or dipping into a container (sink, pail, tub, swimming pools with high chlorine) containing the irritant.
  
  Section::::Causes.
   Section::::Description.
   Treatment for stings may include application of hot water, which has been shown to ease pain. However, multiple theories as to the mechanism of pain relief from hot water have been suggested. A theory that hot water denatures the stingray venom has been questioned because the temperatures required would need to penetrate deeply into the puncture wound and would likely cause thermal damage to surrounding tissue. Other proposed mechanisms include modulation of pain receptors in the nervous system through mechanism such as the gate control theory and the diffuse noxious inhibitory control theory.
   The most common incident regarding humans is strongly connected with "T. draco"’ s typical behaviour: being burrowed in the sand of shallow waters. Especially in the summer it is quite possible for a careless bather to step, jump or fall on the venomous spines of the greater weever. The other occasion where humans are at risk to get stung by "T. draco" is when fishermen are handling the fish if caught in a net.⁠⁠
   The burning heat is usually limited to the soles of the feet, but may extend up to the ankles or lower legs of some patients. The burning can sometimes be accompanied by feelings of 'pins and needles' or tingling in these regions. Nighttime is when almost all sufferers of this syndrome report the heat symptoms being the worst, with the condition getting better as morning comes. Those who have psychosomatic disorders sometimes display psychological symptoms along with the burning of feet associated with the syndrome. For most, there is no redness of the skin of their feet during the heat sensations, and almost never is there accompanying tenderness along with it.
   BULLET::::- Lying on cold surfaces, such as tile floors or in showers (the cold surfaces help ease pain).
  
  BULLET::::- Experiencing pain when urinating
  
  Section::::Pathophysiology.
   Monfreid also wrote in several places about men of his crew suffering stingray wounds while standing and wading into Red Sea shallows to load or unload smuggled wares: he wrote that to "save the man's life", searing the wound with a red-hot iron was necessary.
  
  Section::::Fossils.
   BULLET::::- Repeated application of hot water bottles, heating blankets or heat pads to treat chronic pain—e.g., chronic backache.
  
  BULLET::::- Repeated exposure to heated car seats, space heaters, or fireplaces. Repeated or prolonged exposure to a heater is a common cause of this condition in elderly individuals.
  
  BULLET::::- Occupational hazards of silversmiths and jewellers (face exposed to heat), bakers and chefs (arms)
   Keratolysis exfoliativa normally appears during warm weather. Due to excessive sweating and friction, in for example athletic shoes, the skin can start to exfoliate. Other factors that can cause exfoliation are detergents and solvents.
  
  Another very common cause has been reported from salt water fishermen, who often suffer from these symptoms. It is not sure whether it is from the salt water or whether it is from some bacteria from fish.
  
  Section::::Treatment.
   This condition is caused by an infection of hair follicles due to the bacterium "Pseudomonas aeruginosa". The bacterium is commonly found in hot tubs, water slides, and such places. Children are more prone to this because they usually stay in the water longer than adults. Hot tub folliculitis appears on the skin in the form of a rash, roughly resembling chicken pox and then develops further to appear as a pimple. Hot tub folliculitis can be extremely painful and/or itchy, and left alone without scratching will go away much more quickly. If the rash is aggravated, it can stay, worsen, and spread, lasting for months. By that time, it is much more difficult to treat. The dots usually go away after about 7 to 10 days but the condition leaves a hyperpigmented lesion that goes away after a few months.
   BULLET::::- South Island tomtit "P. m. macrocephala"
  
  BULLET::::- Chatham tomtit "P. m. chathamensis"
  
  BULLET::::- Auckland tomtit "P. m. marrineri"
  
  BULLET::::- Snares tomtit "P. m. dannefaerdi"
  
  Section::::Description.
   BULLET::::- Water has a very high specific heat capacity (4.184 J g K), whereas embers have a very low one. Therefore, the foot's temperature tends to change less than the coal's.
  
  BULLET::::- Water also has a high thermal conductivity, and on top of that, the rich blood flow in the foot will carry away the heat and spread it. On the other hand, embers have a poor thermal conductivity, so the hotter body consists only of the parts of the embers which are close to the foot.
   BULLET::::- "Pacifantistea ovtchinnikovi" (type) — Russia, Japan
  
  Section::::P.:"Porioides".
  
  "Porioides" 
  
  BULLET::::- "Porioides rima" (type) — New Zealand
  
  BULLET::::- "Porioides tasmani" — New Zealand
  
  Section::::R.
  
  Section::::R.:"Rinawa".
  
  "Rinawa" 
  
  BULLET::::- "Rinawa bola" — New Zealand
  
  BULLET::::- "Rinawa cantuaria" — New Zealand
  
  BULLET::::- "Rinawa otagoensis" (type) — New Zealand
  
  BULLET::::- "Rinawa pula" — New Zealand
  
  Section::::S.
  
  Section::::S.:"Scotospilus".
  
  "Scotospilus" 
  
  BULLET::::- "Scotospilus ampullarius" — Australia (Tasmania)
  
  BULLET::::- "Scotospilus bicolor" (type) — Australia (Tasmania)
  
  BULLET::::- "Scotospilus divisus" — New Zealand
  
  BULLET::::- "Scotospilus longus" — Vietnam
  
  BULLET::::- "Scotospilus maindroni" — India
  
  BULLET::::- "Scotospilus nelsonensis" — New Zealand
  
  BULLET::::- "Scotospilus plenus" — New Zealand
  