Postmortem Tanning

An Unusual Postmortem Event

Abstract

A variety of changes, many predictable and others more aberrant, occur during the postmortem interval. A number of these changes are largely influenced by various environmental conditions. We describe 3 cases of an unusual postmortem change associated with prolonged sunlight exposure in both frozen and nonfrozen individuals. In each case, very well-delineated, dark tanning lines were present where clothing or another object blocked sunlight. This change appears distinct from mummification and scant literature references that describe a tanned skin transformation in cases associated with burials in high salt-containing bogs. Collectively, the cases highlight a novel postmortem phenomenon known as postmortem tanning. The potential mechanism(s) of this change is discussed within the context of known observations. Increased recognition and knowledge of postmortem tanning are exceedingly important in assessing how this change may assist in postmortem scene analysis.

Postmortem changes are a direct result of the natural decomposition process that occurs after the death of a human being.¹ Universal identification of certain postmortem changes is important in evaluation of the conditions, timing, and potential events, like body moving, within the postmortem interval.² Approximation of the postmortem interval, defined as the amount of time between an individual's death and the discovery of their corpse is a key component of the forensic autopsy, and postmortem changes play a large role in the process.³ The postmortem change described in this case report, postmortem tanning, has not been well documented in the literature and is not routinely described in standard considerations of postmortem changes. No indexed literature citations and a single image of this phenomenon in an atlas⁴ underscore an incomplete and patchy acceptance of this postmortem change. Improved recognition and documentation of this postmortem change will assist the forensic community in determining the potential role of this change within evaluation of postmortem interval.

We report 3 cases of postmortem tanning, all involving the tanned transformation of skin exposed to sunlight for prolonged periods, producing well-demarcated tanning lines. This phenomenon is distinct from systemic disorders that produce hyperpigmentation (ie, Addison disease); it is also distinctive from other postmortem changes that produce an appearance of tanned skin over the entire body, namely, mummification and bog body formation. Mummification is associated with hot and dry environmental conditions, resulting in a corpse that is dehydrated, brown, hard, and brittle.^3,5 Alternatively, bog body formation, or “dubleon transformation,” involves corpse transformation to a stiff, light brown, shrunken, and moist but dehydrated mass.^6,7 This process is postulated to be accelerated by sphagnan, a polysaccharide found in the moss of salt rich peat bogs, which contributes to chemical reactions that facilitate skin tanning and stiffening.^8,9 Contrastingly, the mechanism behind postmortem tanning is hypothesized to be consistent with traditional tanning, defined as light-induced skin pigmentation secondary to increased and redistributed epidermal melanin.¹⁰

CASE 1

The first case is a 33-year-old Native American woman who was found deceased, completely frozen and partially undressed in early March in the northern plains of the United States. She was last seen outdoors in the early hours of a Sunday morning, approximately 8½ days before being found. The following day, she was transported to our facility.

On initial external examination, the individual was partially covered in snow and ice and completely frozen. Over the next 7 days, inside of our facility and away from direct sunlight, gradual thawing occurred, permitting the completion of an autopsy. The woman was dressed in blue jeans and black ankle socks. Accompanying her but not present on her body was a white tank top, consistent with a partial state of undress secondary to hypothermia-associated paradoxical undressing. A distinct line of demarcation at the location of her jeans could be seen (Fig. 1). Superior to this well-demarcated line, the decedent's skin was found to be darkened in a brownish manner, whereas the skin that was covered by her jeans exhibited no color change. Similar brown pigment transformation occurred in the skin of the decedent's torso, face, and upper extremities, representing postmortem tanning (Fig. 2).

FIGURE 1: Line of demarcation with tanned transformation above location of individual's jeans (case 1).

FIGURE 2: Brown pigment transformation of the decedent's torso and upper extremities (case 1).

Comparable well-delineated, dark tanning lines were found around the individual's ankles, representing an exposed area of skin between her jeans and ankle socks (Fig. 3). In addition, a tanning line was found where a tag on the decedent's jeans had covered a small area on her lower lateral abdomen. Figure 4 displays the initial placement of the tag and the line of demarcation that was found in its place. Final forensic autopsy findings were notable for scattered perimortem abrasions, pulmonary congestion and edema, cholelithiasis, and ethanol intoxication. The decedent's manner of death was deemed an accident caused by prolonged exposure to extreme environmental cold while intoxicated.

FIGURE 3: Line of demarcation existing at the border of the individual's jeans and ankle socks (case 1).

FIGURE 4: Presence of a tag from decendent's jeans with evidence of postmortem tanning lines (case 1).

CASE 2

The second case was a 25-year-old Native American man found deceased beside a roadway after a motor vehicle versus pedestrian collision in early January. The individual was last seen walking outside at around 2:00 am on a Saturday morning and was discovered by local law enforcement at approximately 10:00 pm that night. After the collision, he was exposed to approximately 8 hours of direct sunlight during the short winter days.

When he arrived at our facility, the decedent was wearing a short sleeve black shirt that was positioned halfway up his abdomen (Fig. 5). In addition, the decedent was wearing a black zip-up sweatshirt overlying the t-shirt, gray and black sweatpants, and gray ankle socks.

FIGURE 5: Positioning of individual and portion of exposed skin found on initial discovery (case 2).

Apparent on the individual's torso was a well-demarcated line representing the positioning of his black t-shirt that had shifted upwards during the accident (Fig. 6). The portion of the individual's abdomen that was exposed to sunlight and bitterly cold temperatures for approximately 8 hours exhibited darkened color consistent with postmortem tanning. Final forensic autopsy findings included multiple blunt force injuries including a basilar skull fracture, subdural and subarachnoid hemorrhages, thoracic aortic transection, and hemothorax. The individual's death was presumed to be a “hit and run” case and was classified as an accident by the forensic pathologist. There was no evidence of movement from the impact to the discovery of the body nearly 20 hours later.

FIGURE 6: Postmortem tanning in area where decedent's shirt/sweatshirt had shifted upwards (case 2).

CASE 3

The final case involves a 43-year-old White man who was found in his yard with an apparent self-inflicted gunshot wound to the chest; a rifle and a note of intent were beside his body. This case occurred in the warm summer month of August, in contrast to the previously described cases of postmortem tanning occurring in briskly cold winter conditions. The decedent was last seen by a neighbor approximately 36 hours before he was found deceased outside.

Law enforcement discovered the body, which was dressed in a blue t-shirt, black boxer brief underwear, and tennis shoes (Fig. 7). As displayed in Figure 7, the decedent's t-shirt was found to be rolled up slightly on his abdomen, creating a space of skin that was exposed to prolonged sunlight after the time of his death.

FIGURE 7: Initial discovery of decedent at the scene, showing areas of exposed skin (case 3).

External examination at our facility showed extremely well-demarcated lines where the individual's clothing had been positioned and brownish skin pigmentation in the areas where the skin was not protected by clothing and thus in a direct line of sun exposure. Brownish transformation of the skin could be seen on the decedent's abdomen where a layer of skin was left uncovered and on the decedent's upper extremities that were not protected by the t-shirt he was wearing. In addition, brown pigmentation of the skin was seen on the decedent's legs below the location of his boxer brief underwear (Fig. 8). The individual's feet were protected from sunlight by the tennis shoes he was wearing at the time of his death; thus, another well-delineated line could be seen around his ankles, marking the location of where his sneakers were placed (Fig. 9). Each of these findings is consistent with postmortem tanning secondary to prolonged sun exposure after the individual took his own life.

FIGURE 8: Postmortem tanning and associated well-delineated tanning lines over the legs and abdomen (case 3).

FIGURE 9: Well-demarcated tanning lines of the upper legs and ankles (case 3).

Final forensic autopsy findings were notable for hemothorax, lung lacerations, and heart lacerations secondary to a gunshot wound of the chest. In addition, lymphocytic thyroiditis was present. The individual's death was deemed a suicide by the forensic pathologist.

DISCUSSION

In a living individual, exposure to the sun's ultraviolet A and ultraviolet B (UVB) rays results in the processes of both immediate and delayed tanning.¹¹ Immediate tanning occurs within minutes and can last for up to 1 day. It is postulated to be driven primarily by ultraviolet A light, resulting in the oxidation and dispersion of preexisting melanin granules.¹² Contrastingly, delayed tanning is characterized by increased melanogenesis driven by UVB rays, beginning within days of sun exposure and persisting for up to weeks or months.¹² Specifically, delayed tanning involves UVB-induced DNA damage, which leads to increased expression of p53 and subsequent upregulation of the rate-limiting enzyme of melanin synthesis, tyrosine. It also leads to activation of several keratinocyte-derived melanogenic factors (melanocyte-stimulating hormone, basic fibroblast growth factor, nerve growth factor, proopiomelanocortin).^11,12 Altogether, these responses act to increase melanocyte-facilitated synthesis of melanin. Newly synthesized melanin accumulates within melanosomes, which are then transported to keratinocytes within the epidermis. Here, the melanin surrounds the nucleus and functions to scatter and absorb UV light in an effort to protect keratinocytes from future UV-induced damage.¹²

Among the 3 cases of postmortem tanning discussed in this report, the range of episodic sunlight exposure that each decedent's body experienced ranged from approximately 8 hours to 8 days. In addition, the decedent described in case 1 was found completely frozen and allowed to thaw for 7 days before forensic examination and subsequent discovery of postmortem tanning occurred. Given these time frames, it is evident that ample time existed for the mechanisms of both immediate and delayed tanning to occur. Furthermore, the decedent who was allowed time to thaw in our facility likely had a greater propensity to undergo delayed tanning, as this process traditionally progresses for up to weeks or months.

Whereas the physical appearance of postmortem tanning appears straightforward, the question remains as to how this phenomenon occurs physiologically. Ultraviolet-induced DNA damage and the subsequent activation of various melanogenic factors is an enzyme- and energy-driven process, thus leading us to wonder how this can occur in an individual whose metabolism has ceased. Our primary hypothesis involves the preservation of this process and its underlying enzymes by cold environmental temperatures. Two cases discussed in this report involved a deceased individual who was found outdoors in freezing cold temperatures. Furthermore, one of these cases exhibited a cause of death consistent with hypothermia caused by exposure to bitterly cold temperatures while inadequately dressed.

In general, the processes of decomposition and putrefaction are delayed by the presence of a cool surrounding environment, primarily because of suppression of biological activity in the form of enzymes, bacteria, and insects.^3,13 With that being said, it is possible that the decedents who were discovered in the winter exhibited slowed decomposition and preservation of the metabolic pathways required for postmortem tanning to occur. A further expansion of this hypothesis could include the amplification of the sun's ultraviolet radiation by snow. When present, snow functions to return UV radiation upward to the atmosphere and scatter it back toward the ground, thus increasing overall UV radiation emitted by the sun.¹⁴

Although it is possible that the phenomenon of postmortem tanning occurs as a result of delayed decomposition, prolonged exposure to sunlight, and amplification by snow brightness, it is important to note the single case discussed in this report that did not occur in the setting of cold temperatures or snow. Case 3 involved a decedent who was discovered in the summer month of August, posing the possibility that cold conditions are not required for postmortem tanning to occur. Furthermore, it may allude to additional theories regarding the pathophysiology of postmortem tanning, as decomposition was not delayed by cold temperatures in this case.

In conclusion, the present work reports 3 cases of postmortem tanning. Our current hypothesis is consistent with traditional tanning, characterized by a UV-induced increase in melanin and subsequent perinuclear protection of keratinocytes, as well as possible preservation and amplification of this process by cold temperatures and snow, respectively. However, further insight into the pathophysiology of postmortem tanning is necessary to fully understand the phenomenon. For example, further investigation could include obtaining skin biopsies of postmortem tanned skin with histological examination of regions of tanned skin, unaffected skin, and lines of demarcation. Within this process, observation should be made to identify histologic signs consistent with classic tanning (ie, an increased presence of melanin granules). In addition, an area of further research could include the measurement and comparison of moisture levels within areas of postmortem tanned skin and unaffected skin. This process could be aided with the use of a moisture meter, with the notion that the tanned regions of skin would likely exhibit similar levels of moisture as the unaffected regions of skin, ruling out the possibility of artifactual drying. Lastly, documentation of the UV level while at the scene of death could aid in determining if there was a propensity for postmortem tanning to occur.

Altogether, universal recognition and documentation of postmortem tanning within the forensic pathology community are crucial to define the conditions and relative frequency of its occurrence. Coupled with additional research regarding its pathophysiology, increased recognition of this phenomenon could assist in understanding this postmortem change in general and the specifics of the postmortem interval and environment.