Proposal of facial pigmentary unit and facial hyperpigmentation type for Fitzpatrick skin types II‐IV

Abstract

Background

Studies on facial hyperpigmentation across different facial units are limiting. We aimed to analyze melanin pigmentation images to observe facial pigmentary demarcation lines (FPDLs) and suggest facial hyperpigmentation types for normal individuals.

Materials and methods

3D facial melanin pigmentation images of 173 volunteers were obtained and analyzed for the presence of FPDLs. Pigmentation severity was assessed for each of the thirteen facial pigment units. The images were then grouped according to a pattern of hyperpigmentation to suggest three facial hyperpigmentation types—dark spot, photoaging and post‐inflammatory hyperpigmentation.

Results

Four groups of FPDLs including a novel group I were observed. Nasal, frontal, auricular were the darkest pigmented facial pigment unit, and the anterior neck was the least pigmented. The dark spot type was the most common facial hyperpigmentation type. The photoaging type and the PIH type showed age‐dependent distribution, as the photoaging type was more common among the subjects over 40s, and the PIH type was more common in younger subjects.

Conclusion

Facial hyperpigmentation among healthy individuals with Fitzpatrick skin types II‐IV is often accompanied by FPDLs and categorized into three types. Each type is modeled after the pattern of pigmentation associated with certain dermatological disorders. The practical implications of facial hyperpigmentation types can be resourceful in various fields including prevention and treatment of pigmentary disorders.

1. INTRODUCTION

Pigmentation of skin is determined by the amount of melanin produced by melanocytes. In different races, the amount of melanocytes is the same, but the amount of melanin produced makes a difference in skin color. Melanins are classified into two types; eumelanin and pheomelanin. Darker skin phenotypes have a higher content of melanin and higher eumelanin to pheomelanin ratio compared to lighter skin phenotypes. ¹ , ² This difference in pigmentation is also observed in different body parts, and yet studies focusing on pigmentation across facial parts are rare. In literature, there are few studies focusing on the pattern of facial pigmentation on colored skin.

Pigmentary demarcation lines (PDL) are physiological, abrupt transition zones from deeper pigmented skin to lighter skin. ³ Facial PDLs (FPDLs) are more clearly visible in individuals with medium to dark colored skin. Group F FPDLs were first reported by Malakar and Dhar, ⁴ and group G and H FPDLs were subsequently reported by Somani et al. ⁵ These FPDLs are important in identifying facial areas relatively prone for more pigmentation and diagnosing certain pigmentary disorders.

The intensity and distribution of melanin pigmentation can differ on the same face, even when exposed to identical conditions. Individuals with chronic exposure to sunlight are more likely to have accelerated photoaging of skin and often find actinic keratosis or lentigo, on the temporal, cheeks or periorbital area. ⁶ Post‐inflammatory hyperpigmentation (PIH) on the periorbital area secondary to atopic dermatitis and allergic contact dermatitis are commonly encountered. ⁷ Atopic dermatitis patients are likely to have periorbital hyperpigmentation. There is no reported research on the melanin distribution among different facial zones that manifest varying levels of pigmentation. In the past the severity of skin pigmentation was often assessed clinically by physician's eyes, but with the advent of technological advances, many tools have been developed to visualize skin pigmentation. Photorealistic rendering images of melanin pigmentation enable researchers to determine relative level of pigmentation of the facial skin. The aim of this study was to analyze the facial images depicting melanin pigmentation to observe FPDLs and suggest facial hyperpigmentation types for normal individuals.

2. METHODS

Study population.173 Korean volunteers (110 females and 63 males) with Fitzpatrick skin type II, III or IV participated in the study. The study subjects were aged from 20 to 66 and grouped into five age groups (20s, 30s, 40s, 50s and 60s). Pregnant or lactating women and individuals with a history of being diagnosed with dermatological disorder including pigmentary disorder were excluded from the study. All the subjects visited on June and July 2020. Prior to capturing the image, subjects gently washed their face with an identical foam cleanser and rested for 10 min under constant temperature and humidity condition (22 ± 2°C, 50 ± 5% RH). The study was conducted according to the ethical principles based on the Helsinki Declaration. The ethical and scientific validity of this study was reviewed from DERMAPRO Ltd. Institutional Review Board (certification number: 1‐220777‐A‐N‐02‐DICN20138). All subjects were informed about the purpose of the study and provided written consent prior to participation.

Facial image acquisition. Subjects were photographed under standard lighting conditions afforded by the VECTRA XT system (Canfield, USA). Facial three‐dimensional (3D) images were obtained in three modes (standard color, brown, red), and brown images were analyzed for pigmentation. Six cameras of the hardware capture the stereo images in 3.5 ms and generate a high‐resolution 3D computer model of the subject. This system has been tested for accuracy and reliability. RBX Technology of VECTRA system can represent skin images in terms of melanin and hemoglobin components. The skin image captured by the digital camera is comprised of Red, Green and Blue (RGB) channels. RBX transforms this RGB image into the RBX color‐space, where the Red and Brown channels represent hemoglobin and melanin distributions, respectively. Pigmentary changes are better visualized with RBX Brown image and vascular changes are better visualized with RBX Red image.

Image analysis. Firstly, the brown images were checked for the presence of FPDLs. The inclusion criteria for the facial demarcation lines include the previously reported group F, G and H FPDLs, and any novel group of FPDL. Secondly, facial pigmentation unit was assigned after analyzing the distribution of pigmentation on the face and neck area. Thirteen different pigmentary units were assigned—frontal, orbital, cheek, temporal, zygomatic, nasal, labial, mental, buccal, mandibular, anterior neck, lateral neck and auricular (Figure 1). Each pigmentary unit was given a score from one to seven (1:non‐pigmented, 2:very light, 3:light, 4: intermediate, 5:tan, 6:brown, 7:dark) according to the observed level of pigmentation on the brown pigmentation images. Scores of four and above were regarded as hyperpigmentation. In cases where areas of different pigmentation severity in a given pigmentary unit were observed, the severity of the largest area was chosen as the representative value for the entire pigmentary unit. Two dermatologists reviewed the images separately and the average value was used for the analysis. Lastly, the images displaying a similar pattern of hyperpigmentation were grouped together and facial hyperpigmentation types were determined according to the observed pattern of pigmentation.

FIGURE 1.

Facial pigmentation units across face and neck area

Definition of hyperpigmentation type. The subjects’ images were grouped into three facial hyperpigmentation types—dark spot, photoaging and PIH. Each hyperpigmentation type was associated with characteristic pattern of hyperpigmentation. Dark spot type included hyperpigmentation on the frontal, orbital, cheek and zygomatic pigmentary units. Photoaging type of hyperpigmentation was observed in subjects with hyperpigmentation on the frontal, temporal, zygomatic, nasal and buccal pigmentary units. The PIH type included hyperpigmentation on the orbital, cheek, nasal and labial (Figure 2).

FIGURE 2.

(A) Pigmentation severity index. 1 = least pigmented, 7 = dark pigmented. (B) Schematic representation of the three facial hyperpigmentation types, with corresponding units of hyperpigmentation in brown coloration

Statistical Analysis. Microsoft Excel (Microsoft Corp., Redmond, Wash.) was used to calculate averages and standard deviations.

3. RESULTS

3.1. FPDL

Of 173 volunteers, 18 (10.4%) were Fitzpatrick skin type II, 138 (79.8%) were type III and 17 (9.8%) were type IV. In total, FPDLs were observed in 89 volunteers. Seven volunteers with skin type II (38.9 %), 75 volunteers with skin type III (54.3%) and seven volunteers with skin type IV (41.1%) had at least one PDL in RBX‐Brown image. Four different groups of pigmentary demarcations lines were observed. Group F, G and H FPDLs were observed (Figure 3). A fourth, novel linear PDL that ran along the malar prominence and nasolabial fold was also observed. The observed frequencies for each of the four groups of aforementioned pigmentary demarcations lines were 28% (n = 48), 0.5% (n = 1), 4% (n = 7) and 18% (n = 31), respectively. The incidence of FPDL in this study was slightly higher in females (52.7% vs. 49.2%), and most prevalent in Fitzpatrick skin type III (Table 1). No subjects had coexistence of more than one FPDL.

FIGURE 3.

Facial pigmentary demarcation lines in 3D melanin pigmentation images (highlighted with dashed line). (A) type F. (B) type G. (C) type H. (D) type I

TABLE 1.

Prevalence of facial pigmentary demarcation lines observed in the subjects

	Female (N = 110)	Male (N = 63)	Total (N = 173)
Type F line	29.1% (n = 32)	25.4% (n = 16)	27.7% (n = 48)
Type G line	0 % (n = 0)	1.59% (n = 1)	0.58% (n = 1)
Type H line	6.4% (n = 7)	0% (n = 0)	4.05% (n = 7)
Type I line	17.2% (n = 19)	22.2% (n = 14)	19.1% (n = 33)
Total	52.7% (n = 58)	49.2% (n = 31)	51.4% (n = 89)

3.2. Facial pigmentation unit and severity of pigmentation

The pigmentation severity score from one to seven was assigned to each subject's facial pigmentary unit. In average, the top three most pigmented units amongst all the age groups were nasal, frontal and auricular, with the average score of 4.77 ± 1.14, 4.51 ± 1.01 and 4.36 ± 0.90, respectively, and the bottom three units were anterior neck, buccal and mandibular, with the average score of 2.21 ± 0.90, 2.39 ± 1.05, and 2.63 ± 0.99, respectively (Table 2). The most pigmented facial pigmentation units for each age group were the auricular (20s), the nasal (30s, 50s and 60s) and the frontal (40s) (Figure 4). The hyperpigmented units with the average pigmentation severity score above four were nasal, frontal and auricular for males, and nasal, frontal, auricular and orbital for females.

TABLE 2.

Pigmentation severity scores across facial pigmentary units. SD = standard deviation

Mean (± SD)
	Male	Female	20s	30s	40s	50s	60s	Total
Frontal	4.62 ± 1.11	4.45 ± 0.94	3.94 ± 1.04	4.42 ± 1.16	4.75 ± 1.02	4.81 ± 0.79	4.66 ± 0.72	4.51 ± 1.01
Orbital	3.70 ± 1.09	4.10 ± 1.09	3.44 ± 1.30	4.03 ± 1.13	3.61 ± 1.05	4.50 ± 0.87	4.24 ± 0.69	3.95 ± 1.10
Cheek	3.22 ± 0.91	2.99 ± 0.83	2.89 ± 0.89	3.44 ± 0.81	2.61 ± 0.99	3.33 ± 0.68	3.10 ± 0.62	3.08 ± 0.86
Temporal	3.87 ± 0.77	3.72 ± 0.72	3.36 ± 0.76	3.86 ± 0.64	3.64 ± 0.93	4.19 ± 0.52	3.86 ± 0.44	3.78 ± 0.74
Zygomatic	3.94 ± 1.09	3.93 ± 1.08	2.94 ± 0.71	3.31 ± 0.52	3.83 ± 0.91	4.83 ± 0.77	4.93 ± 0.75	3.93 ± 1.08
Nasal	5.06 ± 1.08	4.61 ± 1.14	4.08 ± 1.20	4.50 ± 0.85	4.61 ± 1.10	5.61 ± 0.90	5.14 ± 0.95	4.77 ± 1.14
Labial	2.44 ± 0.86	3.20 ± 1.04	3.11 ± 1.30	3.17 ± 0.85	2.53 ± 1.08	2.94 ± 0.98	2.86 ± 0.79	2.92 ± 1.04
Mental	2.81 ± 0.96	3.17 ± 0.94	2.75 ± 0.94	2.94 ± 0.89	2.78 ± 0.99	3.47 ± 0.97	3.31 ± 0.81	3.04 ± 0.96
Buccal	2.55 ± 1.07	2.29 ± 1.03	1.28 ± 0.61	2.08 ± 0.65	2.25 ± 0.87	3.28 ± 0.85	3.21 ± 0.68	2.39 ± 1.05
Mandibular	2.84 ± 0.90	2.51 ± 1.02	1.92 ± 0.81	2.36 ± 0.83	2.31 ± 0.92	3.31 ± 0.71	3.41 ± 0.73	2.63 ± 0.99
Ant.neck	2.04 ± 0.83	2.30 ± 0.93	1.58 ± 0.73	2.39 ± 0.84	1.94 ± 0.89	2.47 ± 0.88	2.76 ± 0.69	2.21 ± 0.90
Lat.neck	3.51 ± 0.72	3.60 ± 0.65	3.25 ± 0.65	3.67 ± 0.68	3.28 ± 0.74	3.78 ± 0.54	3.93 ± 0.46	3.57 ± 0.68
Auricular	4.08 ± 0.70	4.52 ± 0.96	4.61 ± 0.90	4.39 ± 0.87	4.47 ± 0.94	4.25 ± 0.99	4.00 ± 0.60	4.36 ± 0.90

FIGURE 4.

Schematic representation of facial hyperpigmentation for different age groups

3.3. Facial hyperpigmentation type

Three facial hyperpigmentation types—dark spot, photoaging and PIH—were observed after analyzing the melanin pigmentation images (Table 3). The dark spot type was the most common facial hyperpigmentation type in all the age groups except in the 20s, and the prevalence ranged from 44.4% to 61.1% in each age group. Photoaging type was absent in 20s and 30s, but the prevalence increased from 13.9% in 40s and reached over 40% in 60s. The PIH type was observed in 55.6% of the subjects in 20s, and the prevalence constantly decreased with the increasing age of the subjects, reaching 6.9% in 60s. In both sexes, the prevalence of facial hyperpigmentation types was similar, as the dark spot type was the most common, and photoaging was the least common type (Table 4).

TABLE 3.

3D melanin pigmentation images for each facial hyperpigmentation type

Type	Subject image
A. Dark spot
B. Photoaging
C. Post‐inflammatory hyperpigmentation

TABLE 4.

Prevalence of facial hyperpigmentation types

	Sex		Age
	Male (n = 63)	Female (n = 110)	20s (n = 36)	30s (n = 36)	40s (n = 36)	50s (n = 36)	60s (n = 29)	Total (n = 173)
Dark spot	47.6% (n = 30)	55.5% (n = 61)	44.4% (n = 16)	55.6% (n = 20)	61.1% (n = 22)	50% (n = 18)	51.7% (n = 15)	52.6% (n = 91)
Photoaging	12.7% (n = 8)	16.4% (n = 18)	0% (n = 0)	0% (n = 0)	13.9% (n = 5)	25% (n = 9)	41.4% (n = 12)	15.0% (n = 26)
Post‐inflammatory hyperpigmentation	39.7% (n = 25)	28.1% (n = 31)	55.6% (n = 20)	44.4% (n = 16)	25% (n = 9)	25% (n = 9)	6.9% (n = 2)	32.4% (n = 56)

4. DISCUSSION

In this study, we analyzed 3D facial melanin pigmentation images to observe the presence of FPDLs and analyze hyperpigmentation types of the subjects with Fitzpatrick skin types II, III or IV. The three types of facial demarcation lines introduced by Malakar, Dhar, and Somani ⁴ , ⁵ , namely group F, G and H FPDLs, were also observed in the subjects of  this study. Group G FPDLs were very rare, as only one subject in this study had the corresponding W‐shaped demarcation lines. Different from the three aforementioned FPDLs, a novel group of PDLs that ran along the malar prominence and the nasolabial fold was observed in a subset of the study subjects. We suggest labeling this type of demarcation lines as group I FPDL. This novel group of FPDLs has not been described earlier. In the current study, the group I FPDL was the second most commonly observed, after the group F FPDL, and the frequency was greater than those of group G and H FPDLs combined. The group I FPDL could be characteristic to the Korean population, but it requires further population‐based research to make a legitimate claim. Somani et al. reported female preponderance of the facial demarcation lines (9% in females vs. 0.75% in males) ⁵ ; however, the sex distribution of the FPDLs was quite even in the current study.

The nasal, auricular and frontal were the top three most pigmented facial pigmentary units, while anterior neck was the least pigmented unit. The difference in the severity of pigmentation can be attributed to many factors, such as exposure to the sun or differences in skin thickness among facial parts. Among many facial parts, forehead, corners of the eyes and cheeks are known to be markedly exposed to sunlight. ⁸ The relatively high pigmentation score observed in the auricular area may be accountable to the general public's habit of applying sunscreen, in which the auricular area is easily missed compared to the other facial areas.

Each facial hyperpigmentation type was designed to reflect a group of areas of melanin pigmentation characteristic to certain dermatological disorders. Dark spot hyperpigmentation type includes areas of melanin pigmentation commonly associated with freckle, melasma, lentigo and acquired bilateral nevus of Ota‐like macules (ABNOM). Melasma is most commonly found in the cheek, zygomatic and nasal area, and ABNOM is primarily found in the zygomatic area. ⁹ Seborrheic keratosis is common in the sun‐exposed areas of the face, ¹⁰ and Shibayama et al. found actinic keratosis to occur preferentially in heavily sun‐exposed areas such as the zygomatic and the nose. ¹¹ Along with periorbital pigmentation, labial pigmentation is an important clinical feature in Asian patients with atopic dermatitis. ¹² A healthy individual with no dermatological disorder but present with areas of pigmentation that fall into one of the hyperpigmentation types can be more prone to development of the dermatological conditions associated with the hyperpigmentation type.

The dark spot hyperpigmentation type was the most prevalent out of the three proposed types in both sexes and most of the age groups. The 20s was the only age group in which the PIH type (55.6%) was more prevalent than the dark spot type (44.4%). In the remaining four age groups the dark spot was observed in more than 50% of the subjects. Unlike the dark spot type, the photoaging and the PIH type showed correlation with age. The photoaging type was absent in the 20s and 30s age groups, and the prevalence increased from the 40s through 60s, displaying a positive correlation with age. The PIH type was the opposite of the photoaging type, as the prevalence constantly decreased showing a negative correlation with age. This change in the pigmentation type according to age can be accountable to many factors such as the total accumulated amount of sun exposure, the higher incidence of dermatologic disorders accompanying PIH in younger individuals, and difference in lifestyle including the usage of sunscreen.

There are other tools to study the amount and distribution of melanin in the face. Reflectance confocal microscopy (RCM) is a non‐invasive tool for analysis of the skin at almost histologic resolution to a depth of 200−300 μm including epidermis and upper dermis. ¹³ Since melanin is the main source of reflectance, melanin is easily visualized as bright structures in RCM images uses an 830 nm laser beam. ¹⁴ RCM is inefficient in obtaining a full picture of melanin distribution as it focuses on a small part of the skin and repeated procedures may be required for enough data to represent the whole face. Mexameter is based on absorption/reflection of the light at, respectively, 568, 660 and 870 nm. ¹⁵ The melanin index is computed from the intensity of the absorbed and the reflected light at 660 and 870 nm. ¹⁶ Mexameter enables comparison between different facial parts, however, repeated measurement may be required for the index value representing a whole facial area due to the minute size of the probe. The VECTRA 3D is also noninvasive and able to produce photorealistic images of melanin distribution without repeated procedures. RBX technology enables the visualization of melanin and hemoglobin distributions in skin, the detection of hyper‐pigmented and vascularized regions. ¹⁷ The contrast in melanin pigmentation severity is easily noticeable and directly applied for analysis without further preparation.

The primary limitation of this study is subjective image analysis of facial pigmentation. In this study pigmentation score greater than four was chosen as reference point for hyperpigmentation, and depending on the observer, the reference point that defines hyperpigmentation could differ. This lack of definite reference point for hyperpigmentation is partly accountable to the absence of measurable values in the 3D melanin pigmentation images in the study to objectively assess the level of melanin pigmentation. Moreover, considering the 3D nature of the images, facial curvatures and shades could create a difference between the perceived and the actual level of pigmentation. Due to the location of the center and small sample size, we were only able to recruit the subjects with Fitzpatrick skin types II, III and IV. Future studies with a larger sample size including all the skin types would enable comparison of hyperpigmentation patterns among different skin types.

This study analyzed the pigmentation severity and the pattern of pigmentation distribution in healthy individuals. With the results of the analysis, we introduce a novel group of FPDL and suggest three facial hyperpigmentation types, dark spot, photoaging and PIH that can be applied to categorize normal individuals on the basis of facial hyperpigmentation. The virtue of this study is that in author's knowledge, it is the first study to suggest facial hyperpigmentation type for healthy individuals. Facial hyperpigmentation type can have a variety of application in the real world setting. Predicting areas of possible PIH and providing information to patients on preventive care, reinforcing instruction manual for skin‐whitening products with more targeted approach, and selecting specific areas for laser treatment for pigmentary disorders based on the suggested types for better outcome are just few examples of areas where this study can be useful outside the laboratory setting.

5. CONCLUSION

By analyzing 3D melanin pigmentation images, we were able to observe a novel facial demarcation line and suggest three facial hyperpigmentation types for normal individuals with Fitzpatrick skin types II, III or IV. Further research in larger sample sizes among different races would produce a more accurate facial pigmentation pattern of normal individuals and consolidates the proposal for both the presence of the novel group of FPDL, and the facial hyperpigmentation types.

Oh S‐M, Lee YE, Ko MJ, Baek JH, Shin MK. Proposal of facial pigmentary unit and facial hyperpigmentation type for Fitzpatrick skin types II‐IV. Skin Res Technol. 2023;29:e13251. 10.1111/srt.13251

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.