Frostbite of the face and ears: epidemiological study of risk factors in Finnish conscripts

Introduction

Local cold injuries are a common problem of military operations and training in wintertime, especially during land manoeuvres.1 2 Feet and hands are most prone to cold injuries, but the unprotected areas of the head—ears, nose, and cheeks—are also vulnerable to cold.3

In addition to the ambient temperature, other factors influence the risk of developing frostbite of the face and ears. The wind (windchill effect) greatly affects heat loss from the skin by convection.4 5 Preventive behaviour and protective clothing diminish the risk.6 7 Protective ointments are traditionally used,8 but their role is controversial.9

Exposure to cold is part of outdoor training for the Finnish defence forces in winter, both at garrisons and during manoeuvres. We evaluated the incidence of and risk factors for frostbite of the face and ear in Finnish conscripts during military service.

Subjects and methods

In Finland all healthy men are required to serve in the army for 8-11 months in peacetime. Each year 25000-35000 male conscripts (mean age 19 years) are trained. After an exceptionally hard winter in 1976 the Medical Section of the Finnish Defence Staff started systematically collecting data on all cold injuries that needed medical examination.10 Information on weather, type of activity, and other conditions at the time of the injury, as wellas the medical facts, were given by local medical officers. Information on clothing, shoes, use of protective ointments, fatigue, previous cold injuries, sensitivity to cold and the degree of sweating at the extremities, smoking, earlier indoowork, and so on was given by the injured man. When possible, two conscripts who had not developed frostbite were randomly selected from the same squads as the injured soldiers to act as controls. Valid controls could not always be found as the injured man was sometimes alone when he was frostbitten.

The severity of frostbite can be assessed only in warm surroundings and some time after the injury—from several hours up to two days after the typical physical signs of early frostbite (local blanching of the skin with clear demarcation from unaffected skin). In grade I frostbite the skin is reddish and oedematous, in grade II frostbite it starts to blister and form bullae, and in grade III frostbite local necrosis of the dermis develops over 1-2 weeks.11

BMDP software was used for the statistical analysis. Univariate analysis was used to determine which variables had an effect, the proportions in injured and control groups being compared by using a ² test. Thereafter a logistic stepwise regression model was used to avoid unnecessary multiple colinearity. In the final analysis a fixed module was used,with calculation of the odds ratio to measure the degree of risk. All tests were two sided, and all controls were handledas one group.

The risk factors evaluated were

• The type of activity at the time of being frostbitten—land manoeuvres for up to two days or for three or more days, on duty at garrison, off duty at garrison, on leave

• The degree of physical activity at the time of injury—physically active outside, waiting on site, being transported (fig 1)other

• Fatigue

• Physical condition—the result of a 12 minute running test

• Wearing of scarves

• Wearing of earflaps

• Application of protective ointments

• Smoking—whether a smoker before the frostbite

• Working outdoors as a civilian

• Sensitivity of hands and feet to cold

• Profuse sweating of hands and feet.

Fig 1

Typical high risk conditions for developing frostbite of the face: soldiers in tow on a motor sleigh

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Results

During 1976-89 a total of 2054 men reported frostbite, 913 (44%) of them having frostbite of the face or ears (head). A total of 2478 non-injured conscripts acted as controls. The annual number of cases of frostbite of the head ranged from 17 to 234 (13% to 64% of all cold injuries), being highest during the coldest winters. The mean annual incidence of such cases was 1.8 per 1000 conscripts (95% confidence interval 1.3 to 2.3 per 1000).

Frostbite mainly affected the ears (533 conscripts (58%)), then the nose (201 (22%)) and other regions of the face, mostly the cheeks (183 (20%)). Most cases were mild (grade I; 803/913 (88%)). In the coldest winters, and especially during army exercises, up to a third of cold injuries were grade II (fig 2. Noses were most prone to second grade injuries. Grade III frostbite occurred only sporadically.

Fig 2

Grade II bullous frostbite of the upper part of auricle

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Table 1shows the prevalence of frostbite during different types of activity. Most frostbite of the ear and face occurred when soldiers were serving at a garrison (while on guard, practising shooting, handling weapons, participating in outdoor sports, etc) and while they were on leave. Only 196 of the 913 conscripts (21%) developed frostbite during land manoeuvres. Frostbite of the ear occurred more often on leave than on exercises (213/533 (40%) v 61/533 (11%)). Frostbite of the ear was the most common cold injury in conscripts on leave (prevalence 89% (213/249)).

Table 2shows the major risk factors for frostbite of the face and ear. It shows how important earflaps are in protecting the ears. Using a scarf protects both ears and cheeks surprisingly well. When we analysed the risks during land manoeuvres separately, increased sensitivity to cold (odds ratio for developing frostbite of the nose 3.4 when fingers have increased sensitivity to cold and 3.5 when toes have increased sensitivity to cold) and working indoors as a civilian (1.9 for frostbite of the cheek) became additional risk factors.

The use of protective ointments increased the risk of developing frostbite of the head threefold to sixfold. In the whole sample of 2054 conscripts with frostbite, 345 (17%) had used them. Of the 913 conscripts with frostbite of the head, 143 (16%) had used them. Most patients with grade II frostbite had used emollients (98/109; 90%).

The data on weather conditions were insufficient to analyse the chilling effect of the wind on the development of frostbite. Neither smoking nor tiredness correlated with frostbite of the face or ear.

Discussion

We studied over 900 largely mild cases of frostbite of the face and ears. We sought to differentiate risk factors as independent variables, and our results show the importance of protective clothing, especially earflaps and scarves. The effect of the type of activity on cold injuries can also be explained mostly by the different clothing worn. During manoeuvres every soldier wears a combat suit with appropriate winter cap (3, the clothing differing only in minor details such as type of underwear and socks, etc. On or off duty at a garrison soldiers wear either combat suits or light uniforms. On leave most men wear civilian clothes and often seem not to wear hats with earflaps.

Fig 3

Young conscript in his winter outfit during land manoeuvre at −32°C. Notice the frozen villus hairs on cheeks

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The increased risk of frostbite with the use of protective ointments was unexpected but consistent for all grades of frostbite of the face and ear. Thus the quality of ointments used was not registered. The use of emollients may give a falsefeeling of safety, and the skin is therefore left unprotected. The preliminary results of tests in a cold chamber support this possibility.9

Conscripts, and also their leaders, should be educated about how to prevent cold injuries7 12 13: appropriate clothing should be worn on leave as well as on duty. Frostbite of the face and ears can develop insidiously. The first symptoms of frostbite are a localised sense of coldness, followed by local stinging and tenderness. Then the affected part becomes numb. At this stage the skin to an observer looks blanched, with sharp demarcation from the normal surrounding tissues. However, the affected person at this time cannot see the blanching and is unaware of the injury. Thus soldiers need to be taught the early signs and symptoms of frostbite.

CONCLUSION

Cold injuries to the ears and face are mainly caused by not wearing appropriate clothing. Wearing a scarf and a warm cap with earflaps reduces most of the risk. The unexpected risk connected with the use of protective ointments indicates that the routine use of protective ointments cannot be recommended.

We thank the Illustration Centre of the Defence Staff for permission to use the photographs.