Minimal Erythema Dose (MED) Testing

The overall goal of the following experiment is to conduct minimal erythema dose testing in order to determine the lowest dose of ultraviolet radiation that will cause erythema when administered to an individual. This is achieved by first preparing the light source and participant for UV exposure. As a second step, the participant is exposed to UV for varying durations, which may cause erythema, also known as sunburn.

Next, changes in skin color are assessed in order to determine the minimal erythema dose results are obtained. The show variation in skin darkening across exposure times of individuals based on visual inspection and spectrometry. My name is Susan Darlow.

I'm a postdoctoral fellow in the laboratory of Dr.Carolyn Hackman. Demonstrating the procedure will be Tasia Munchie, a research assistant in Dr.Hackman's lab. I will be demonstrating the research participant role Begin this procedure by explaining to the participant how minimal erythema dose or MED testing works.

So I'm going to expose some skin of your skin to your V light for almost 20 minutes and tomorrow we're gonna check the section of the skin to see how sensitive you're to the light. You may experience burn in some parts of that skin, which was exposed to uv, and if it is painful, you can treat like any other sunburns you would have. Once the procedure has been explained, both the staff and participant put on UV protective glasses, then expose the forearm of the participant.

Next, remove the dalin patch backing on the left and right sides of the patch and place it on the inner lower arm. Avoid any existing skin blemishes when placing the patch. Have the participant put on a protective glove, cover any additional skin on the arm with the participant's shirt or other material in order to protect those areas from UV exposure.

The next step is to position the participant's arm so that the holes in the patch will be in alignment with the UV light source. Double check that no other skin will be exposed to the UV light. Once the participant's arm is in the correct position, inform them that they will feel warmth once the experiment begins, but ensure them that their arm will not be burning during the test.

Prior to beginning UV exposure, select the total duration of the exposure based on the manufacturer's specifications for the light source and the participant's Fitzpatrick skin. Type on a scale from one to six on this scale. One represents very fair skin and six represents very dark skin.

Then set a timer for the total duration of UV exposure. This participant has a number three skin type, and their exposure time will be 20 minutes. A second backup timer may also be used.

Next, remove the covering over hole one on the dalin patch. Turn on the UV light source and start the timer. Uncover subsequent holes on the patch at timed intervals during UV exposure for a 20 minute exposure.

Open hole number two after two minutes, hole number three after four minutes. Hole number four after eight minutes. Hole number five after 12 minutes and hole number six, after 16 minutes following UV exposure, mark the scan exposed on the far edge of the first and last holes of the patch with a small dot.

In order to more easily identify the exposed areas after 24 to 48 hours, ask the participant to not wash off the marks until after the skin has been examined. Then have the participant remove the glove and patch. Then remind them to return in 24 to 48 hours for the skin to be reexamined.

Please be sure to make come back tomorrow so we can test the results. After 24 to 48 hours. Examine the exposed areas of skin.

Red or pink skin indicates erythema or burning. Erythema to skin exposed to the shortest duration of UV is defined as the minimal erythema dose or MED placed the patch back on the skin using the small dots in the corners of holes. One in six to position the patch back onto the exposed skin in order to identify the different regions.

Once the exposure areas have been identified, place the spectrophotometer aperture in the center of the first hole to be measured. Then measure each of the six exposure areas in numerical order. Next, measure one unexposed area near the others.

For comparison, avoid freckles, moles, or other non UV related discolorations. Spectrophotometers provide measures of L star, which represents darkness and B star, which represents hue. A star refers to the redness of the skin.

An increase in Astar indicates redder skin and should correspond with increases in UV exposure duration. If astar values do not increase with the increase in UV exposure, duration remeasure the values that are not in corresponding order shown here are typical results seen 24 to 48 hours after UV exposure. The markings left after the experiment assist in aligning the patch, which will be placed back on the arm during spectro photometric measurements of each region.

In order to determine the minimal erythema dose spectrophotometer readings are taken and the ASTAR values are calculated for each region, the minimal erythema dose is calculated as being the time of exposure that causes an increase in astar greater than 2.5 above baseline. For this participant, it was 18 minutes of exposure. If the data in the table appears to be out of order, repeat the readings.

Taking care not to analyze areas with skin blemishes or areas that are abnormally darkened. In this case, the baseline or NA value is 9.0, but it should be less than that of the four minute duration which read 7.2. After watching this video, you should have a good understanding of how to conduct minimal erything dose testing.