IR Analysis of the Effect of a Spray Cooler on Human Skin

Carlo Sansotta^a, Barbara Testagrossa^a, Raffaele Novario^b, Giuseppe Acri^a, Maria Giulia Tripepi^a, Giuseppe Vermiglio^{a a} Di. P.A.S.S.I. – University of Messina (ITALY) ^b University of Varese (ITALY)

ABSTRACT

To avoid skin damage due to sun exposure, it is a good idea to protect the body from UV radiation with sunblock or sunscreen. Such products reduce the amount of UV radiation able to reach skin tissue and cause damage. In addition, there are new products that can help to alleviate the effects of a first degree burn, which affects only the epidermis and can happen very quickly. One of these post-burn products is a sprayable foam which causes the burned area to cool very quickly. The presenters investigated the action of these burn relief sprays in relation to their IR transparency. They wanted to define skin behavior after their application and make sure there were no dangerous side-effects. The authors will present the results of their experiment conducted with healthy, voluntary subjects.

INTRODUCTION

The vast majority of skin cancers are due to unprotected ultraviolet radiation (UV) exposure. The sun is the main source of UV. The broad spectrum and intensity of UV from the sun are due to the high temperature at its surface as well as its size.

UV penetrates into the dermis, exposing a variety of cells and structures, depending in part on the thickness of the human stratum corneum and epidermis. It reduces the stretchiness of the skin and can cause premature aging and wrinkling, as well as the formation of age spots. Deeper in the skin, it causes changes in the structure of cells, and increases the risk of skin cancers.

The short-term results of unprotected skin exposure to UV rays are sunburn and tanning. Progressive acute effects of exposure to sun radiation are solar erythema before, afterwards “sunburn”, which consists of a reddening of the skin that appears up to 8 hours after exposure to UV and gradually fades after a few days. Severe sunburn can cause blistering and destruction of the surface of the skin, with secondary infection and systemic effects, similar to those resulting from a first or second degree heat burn. When sunburn occurs, it is necessary to avoid direct sunlight by covering up and staying in the shade, until the sunburn has healed, or cool the skin by sponging it with tepid water or having a cool shower or bath. In some cases application of special burn cream must be necessary.

Recently, new products have been designed to help alleviate the effects of first degree burns, either due to sun exposure or to body contact to hot fluids or objects. Some of these post-burn products are sprayable foams, which cause the burned area to cool very quickly. In this paper we investigated the action of these burn relief sprays in relation to their IR transparency and effect duration, in order to monitor skin behavior after their application and assess the risk due to possible related effects.

MATERIALS AND METHODS

To carry out our investigation, we used a FLIR ThermaCAM PM695 infrared (IR) camera. We utilized it in a room with controlled and stabilized microclimatic conditions. In our protocol, conditions were as follows:

Temperature: 22.0°C ± 0.1°C

Ventilation: 0.3 m/s ± 0.2 m/s

Relative humidity: 48% ± 1%

Distance camera/subjects: 0.48 m ± 0.01

We conducted our investigation on healthy volunteers, and in each subject we selected their right forearm as the area to be treated with post-burn products. At first, the subjects were acclimatized to the room with their arms uncovered for at least 15 minutes. Then, the right arm was positioned over a polystyrene surface, which had been selected because of its thermal properties. Our measurements were conducted with commercially available products. The tested products, which are usually applied as an early treatment of minor burns, consist of special sprayable foams primarily intended for a rapid cooling and therefore local pain relief. They contain hydrocarbons and propellant, but their exact composition is never available. Their directions for use indicate that the cooling effect of these burn relief sprays starts immediately after application and continues for up to two minutes, while the presence of propellants reduces the temperature of the affected area below approximately 9°C.

Before carrying out the in vivo measurements on human subjects, we carried out some preliminary studies on the cutaneous surfaces of guinea pigs, which were depilated and immobilized for IR investigation, in order to identify the results and to check out the investigation protocol for use on human beings. The results obtained encouraged us to try our experiment on healthy volunteers, both male and female, and the results of this investigation, corroborated the previous ones.

We sprayed the products being tested on the selected forearm of a suitable number of healthy subjects. For each subject, we took two pictures: one on the IR region of the spectrum (basal thermogram) and the other one in the visible region of the spectrum (ordinary photo). After that, we vaporized the sprayable foam on the skin and took a sequence of IR pictures at 30 second intervals. The average time required to reach the basal thermal condition was about 30 minutes, so the pictures were taken for no less than this time. On readings taken for each voluntary subject who underwent the thermographic tests, we calculated the weighted mean of the area extension. With this aim, the thermographic pictures were transferred from the ThermaCAM to a hard-disk and then examined using a dedicated workstation equipped with Intel Pentium IV processor and Image-Pro plus software from Media Cybernetics. This software was able to perform the most common basic operations on the selected images in a native way and let the operator write his own calculus routines, since it is possible to write macros in a proprietary programming language. We applied an algorithm, called “IMI – Image Mean Index”, defined as follows:

R_i ⋅ a_i

IMI = _∑

iA where Ri represents the weight associated to every area ai and A is the sum of all the ai areas. The use of this algorithm permits to associate a single number to every picture, so that we obtain a numerical sequence to build the diagram of thermal behavior versus time. In addiction, we selected a Region of Interest (ROI), which was the same for all the IR pictures, then measured the temperature mean value of these ROI’s in order to follow the temperature behavior versus time.

RESULTS

The results of the thermographic survey are shown in the following figures and graphs. Figure 1 shows the area that we have chosen for our investigation (Figure 1a is the IR image, whereas in Figure 1b the same image is reported, but in the visible region of the spectrum), showing the typical right forearm image of healthy volunteers who underwent the treatment. The area selected was the zone near the elbow, because it is relatively wide and hairless. In addiction, this area is rich in large blood vessels, so the thermal dispersion is very significant.

Figure 1a. Reference (basal) IR image of the right forearm Figure 1b. Reference image of the right forearm selected selected for testing the post-burn product. for testing the post-burn product in the visible region of

the spectrum.

Figure 2 shows the same area of investigation immediately after the burn relief spray was applied, as it appears in the IR region of the spectrum (figure 2a) and in the visible one (figure 2b). As expected, the treated area appears to be significantly cooler than the surrounding one.

In Figures 3-5, we report the thermographic behavior of the treated area at 10 minute intervals. It is possible to notice the return to the thermal irradiance which reached the initial condition about 30 minutes after the application of the post-burn product under test.

Figure 3. The treated area with the post-burn product sprayed on it, after 10 minutes, as it appears in the IR region of the spectrum and in the visible one.

Figure 4. The treated area with the post-burn product sprayed on it, after 20 minutes, as it appears in the IR region of the spectrum and in the visible one.

Figure 5. The treated area with the post-burn product sprayed on it, at the end of the treatment, as it appears in the IR region of the spectrum and in the visible one.

In Figure 6, the curve shows the trend of the IMI mean value (in arbitrary units) versus time (at 30 second intervals) which has been calculated as mean of the single values obtained for all the subjects. The cooling down and the following return to thermal balance is also evident. Figure 7 reports the behavior of the mean temperature of a selected ROI versus time. The reported trend shows the return to thermal original conditions.

At the end, we have verified if the application of the tested sprayable foams could determine any alteration on skin emissivity, owing possible affections due to chemical reactions foam induced. In fact, the emissivity affects the temperature values, thermographically measured and can be determined by comparing the thermographic temperature values with the thermometric ones. To this aim, at first, we have determined the temperature of the skin surface by using a digital thermometer. So, we have calculated the ratio between the thermographic and thermometric temperature in a selected ROI. At thermal equilibrium, the temperature measured by the thermometer was equal to the thermographic temperature, in correspondence of the same ROI. Then, we have repeated the same control at 2 minute intervals, and we have reported the results of this elaboration in Figure 8. The curve shows the trend of the ratio between the thermographic temperature and the thermometric one versus time.

Calculated IMI

0 200 400 600 800 1000 1200 1400 1600 1800 2000 time (seconds)

Figure 6. The Image Mean Index (IMI) as calculated on the typical images series. On Y axis the calculated IMI mean values (arbitrary units); on X axis the time (seconds).

Mean Temperature vs. time

Mean Temperature (°C)

35.00

30.00

25.00

20.00

15.00

10.00

5.00

0.00

Figure 7. The mean temperature as calculated on the typical images series. On Y axis the IR mean temperature (°C); on X axis the time (seconds).

Time dependance of temperature ratio

0 5 1015 20253035

time (minutes)

Figure 8. The time dependence of the ratio between the thermographic temperature and the thermometric one. On Y axis the temperature ratio; on X axis the time (minutes).

DISCUSSION AND CONCLUSIONS

The results of the analysis conducted on these post-burn products show that their application enables the treated area, cooled down to low temperatures ranging about 10 °C, to completely return to normal condition about 30 minutes later, as enhanced after evaluating both the calculated IMI curve and the mean temperature one versus time. So, the tested products act on human skin for this length of time, cooling the cutaneous tissue as required.

In addiction, the analysis we have conducted on the possible modification of the skin emissivity induced by tested sprayable foams, enables us to highlight that the emissivity does not decrease, as enhanced by the final measured ratio between the IR camera detected temperature and the thermometric one, which does not vary with respect to its initial value. So, it is possible to exclude side-effects related to foam induced chemical reactions affecting IR properties of the skin tissues.

SUMMARY

We tested some burn relief products that can be used to help alleviate first degree burns due either to sun exposure or to body contact to hot fluids or objects. The test conducted on healthy volunteers have shown that their application on skin tissues have allowed a quickly cooling with the return to initial conditions after a reasonably period of time without modifying the IR properties of skin.

REFERENCES

World Health Organization; “Environmental Health Criteria 160 – Ultraviolet Radiation”; pp 46-47; Proc. Thermosense XXII; SPIE Vol. 4020; April, 2000

Sansotta, C.; Testagrossa B.; Novario R.; Tripepi M. G. and Vermiglio G.; “Thermographic investigation of clinical spray film for medical hand-wraps”; pp. 307-312; Proc. InfraMation 2005; Vol. 6; October, 2005

Sansotta C.; Vermiglio G. and D’Angelo G.; “Conduzione termica dei bendaggi impiegati nella terapia delle ustioni”; pp. XX; Proc. LXXVI Congresso Nazionale SIF, Trento (I); 1990

Vermiglio, G; Sansotta, C. and Ruello, E; “Approccio teletermografico al trattamento delle ustioni cutanee”; pp. XX; Proc. Progressi della Scienza e della Tecnica in medicina estetica; Palermo (I); 1991