Frostbite

Frostbite is exactly what the word says: tissue freezes, ice crystals form in the skin and in what lies beneath it, and cells die. The dangerous part is that the process gives no warning. The freezing area hurts at first, then goes numb, and from that moment there is no signal left telling you to get indoors. People come home convinced they were merely cold and grasp how serious it was a day later, when the blisters appear. Yet it is the first few hours that decide whether the fingers or toes are saved, and they are decided by simple actions that are very easy to get wrong.

What the cold does to tissue

In the cold the blood vessels of the skin close down to hold on to heat, and blood withdraws from the edges towards the heart. The parts that go longest without a blood supply are the ones that stick out and are least protected: fingers, toes, the tip of the nose, the ears, the cheeks, the chin. Once the tissue is cold enough, the water between the cells freezes, the crystals tear the cell walls, and thickened blood plugs the small vessels. The second wave of damage arrives on thawing, which is why the way it is warmed matters so much.

Cold rarely acts alone. Things that speed it up:

• wind, which strips away the layer of air already warmed by the body: in a strong wind skin freezes several times faster than at the same temperature in still air;
• wet: soaked socks and gloves, skin sweating under a snowsuit;
• tight boots, snug gloves, tight lacing, rings and bracelets — anything that gets in the way of the blood;
• alcohol and smoking: the first opens the skin vessels and lets heat go while dulling the sense of cold, the second closes the fine vessels of the fingers;
• conditions in which blood reaches the extremities poorly: diabetes, arterial disease of the legs, Raynaud's phenomenon;
• tiredness, hunger, dehydration, altitude and sitting still;
• a previous frostbite injury: those patches feel the cold more easily for the rest of your life.

Children and older people deserve a separate word. A child loses heat faster and may simply not think of saying that the fingers have stopped feeling anything. An older person often does not register the cold at all and rewarms less well unaided.

Telling mild from serious

The difference is not obvious straight away, but the rule is simple: the less the skin feels and the harder it is, the worse it is.

Surface chilling. The skin pales, tingles and burns, then goes slightly numb but stays soft. In the warm it reddens, stings and returns to normal within a few hours leaving nothing behind. This is not yet frostbite but a warning.

Superficial frostbite. The skin is white or waxy, cold to the touch and without sensation, but beneath the top layer the tissue is still soft and dents under a finger. On warming come severe pain, redness and swelling, and within the first day blisters with clear or slightly cloudy fluid. Those blisters are a good sign: the deeper layers are alive.

Deep frostbite. The area is hard as wood and does not dent at all, and the skin is white with a bluish or mottled cast. Sensation is gone completely, even deep pressure is not felt. Blisters come later, small and blood-filled, or they never come. After some days the tissue darkens and dries out.

On brown and black skin the redness and the bluish tinge are harder to see: go by hardness, swelling and loss of sensation rather than by colour.

What to do in the first hours

There is not much to do before medical help arrives, but it needs doing properly.

• Get indoors, or at least out of the wind. Take off wet clothing.
• Remove rings, bracelets, watch and tight boots at once: everything is about to swell and then they will not come off.
• Rewarm in warm water at roughly body temperature, no hotter. Test it with the good hand or an elbow: it should feel pleasant. Keep the part in until the skin softens and turns pink again, which usually takes around half an hour.
• If there is no water, use body heat: hands under the armpits, someone else's feet or face between your palms.
• Rewarming hurts a great deal, and that is normal. Ordinary over-the-counter painkillers help; ask a doctor or pharmacist which one suits you. Children and teenagers are not given aspirin.
• Afterwards pat the skin dry, put dry gauze between the fingers or toes, cover loosely with a dressing and raise the limb so it swells less.
• Give a warm drink and wrap the whole person up: it is not only the fingers that are cold.

What must not be done:

• rubbing, whether with a hand, a mitten or, worst of all, snow: the ice crystals inside the tissue slice through cells as you rub, and snow adds cold and dirt;
• warming at a fire, radiator, heater, hairdryer or hot water bottle: numb skin does not feel the heat, and a burn is added to the frostbite;
• thawing the part if the person still has to be moved through the cold and could freeze again: a cycle of thawing and refreezing damages tissue far more than uninterrupted cold;
• walking on frozen feet if it can be avoided at all;
• opening or trimming the blisters;
• drinking alcohol or smoking.

When to call an ambulance

Call an ambulance (across European countries the single number is 112) or take the person to emergency care if:

• the area is hard and does not dent, and the skin looks white, blue or mottled;
• sensation does not come back after rewarming;
• blood-filled blisters have appeared;
• the frostbite covers a large area, or a whole hand, foot or the face;
• the surrounding skin turns red and hot, or there is pus, red streaks or fever: that is infection;
• the person is a child, an older person, or someone with diabetes or arterial disease.

Separately, look for signs of hypothermia, which matters more than any frostbite and is dealt with first: the person shivers uncontrollably for a long time and then abruptly stops shivering, speech slurs, movements grow clumsy, and drowsiness, indifference and confusion set in. Such a person must not be left alone or allowed to fall asleep: cover them, get them out of the cold, take off wet clothes and keep talking to them until help arrives. Rubbing and vigorously moving the limbs is not appropriate here.

What doctors do next

In hospital the whole person is rewarmed first and the pain is dealt with: when it is severe, prescription painkillers are needed, because the household ones are not equal to it. The depth is then assessed and, in severe injury, the blood flow is imaged to see how far the circulation reaches.

There is one thing worth knowing in advance: in severe frostbite, in specialist centres and within the first hours after rewarming, drugs are used that dissolve the clots in the small vessels or open them up. This greatly reduces how much has to be amputated later, but the window is measured in hours. So with a hard, insensate area it is better not to wait until morning, but to find out where to go.

Beyond that: care of the blisters, dressings, a check on tetanus immunisation, antibiotics if infection sets in, and physiotherapy so the joints do not stiffen.

Surgery, where it is needed, is not rushed. The line between living and dead tissue is not visible straight away, and it is left to declare itself, which takes weeks and sometimes months. The wait is uncomfortable, but it saves more in the end.

What is left afterwards

Mild cases leave nothing behind. After a more serious injury there is often a tail:

• heightened sensitivity to cold, sometimes permanent: those same digits start to blanch and ache in weather nobody else notices;
• numbness, pins and needles, pain at rest, and excessive sweating of the area;
• nails that grow deformed or stop growing;
• stiffness and early wear of the finger and toe joints.

Children carry a particular risk that parents should know about: cold damages the growth plates in the bones of the fingers and toes, and this can show up years later as a digit that grows short or crooked. That is why frostbite in a child is worth showing to a doctor even when everything appears to have passed off well.

Keeping it from happening

• Dress in layers: the inner one moves moisture away, the middle one insulates, the outer one keeps out wind and water. One thick jumper works less well than three thin layers.
• Mittens are warmer than gloves, because the fingers heat one another. Keep everything dry, carry spare socks and gloves and change them at the first hint of damp.
• Neither boots nor gloves should press. A tight boot gets colder than a roomy one, however warm it looks.
• Cover the face and ears: a hat with ear flaps, a collar or neck warmer, a hood against the wind.
• Eat and drink: the body burns far more energy in the cold, while thirst is less than the need. Keep moving and wiggle the fingers and toes, and do not stand still for long.
• Watch the wind as well as the thermometer: in a strong wind a moderate frost is more dangerous than a hard one in still air. No alcohol before going out or while out.
• Check on children yourself and bring them in to warm up every half hour: they get carried away and do not complain.
• On long winter journeys keep a blanket, warm clothes, water and a charged phone in the car.

Online consultation

Remotely it makes sense to go through a mild case that has already been rewarmed: what the skin looks like, what to expect over the next day, whether it needs dressing, what to do about blisters that have formed, and at what point to be seen in person. The doctor will explain how to look after the area so it does not become infected, why the pain increases after rewarming, and will weigh the risk of complications given diabetes, smoking and the state of your arteries. It is also a convenient way to discuss the legacy of an old frostbite injury, the fingers that are permanently cold and painful. A hard, insensate area, blood-filled blisters and signs of hypothermia are not assessed through a screen: those call for face-to-face care immediately.

This material is for information only and does not replace medical advice.