Ethnobotanical Studies on Traditional Medicinal Plants Used in the Treatment of Humans’ Skin Diseases in Ethiopia: A Review

Ethnomedicinal Research in Ethiopia

Before three and a half decades in Ethiopia, it was stated that detailed descriptions of plants used medicinally were scanty (FAO, 1986); however, few ethnobotanical investigations were conducted in the recent past in different parts of the country [4, 12, 13, 14, 15, 16]. These researchers have clearly indicated the presence of a wealth of indigenous knowledge of the use and management of plant resources among the local people of various parts of the country and ethnic groups. Nevertheless, considering the country’s varied flora and socio-cultural diversity, these studies are few as ethno-medical healing systems vary across cultures. In addition, researchers have also indicated the reliance of nearly 80% of the population in the country on utilizing plant-based traditional medicines as a major health-care system [17].

Common Dermatological Disorders

It was reported that skin is primarily an organ of protection. As the body’s first line of defense, the skin is continuously subjected to potentially harmful environmental agents, including solid matter, liquids, gases, sunlight, and microorganisms [18]. Although it has remarkable properties that allow for a continuous cycle of healing, shedding, and cell regeneration, the skin is subjected to a very wide range of disorders [19].

Infectious Skin Disorders

Mitscher LA, et al. [18] indicated that the skin is subjected to attack by a number of microorganisms. Normally, the skin flora, sebum, immune responses and other protective mechanisms guard the skin against infection. Depending on the virulence of the infecting agent and the competence of the host’s resistance, infections may result [18]. Bacterial Infections Bacteria are considered normal flora of the skin. Most bacteria are not pathogenic; however, when pathogenic bacteria invade the skin, superficial or systematic infections may develop. Bacterial infections are classified as primary, or superficial (e.g., impetigo), and secondary, or deep (e.g., infected ulcers) [18]. The most common bacterial infections include impetigo, folliculitis, furuncles, and carbuncles [18, 20].

Fungal Infections

Microbial information revealed that fungal infections of the skin can be superficial, intermediate, or deep. Some are opportunistic and affect a susceptible host, while others are truly pathogenic and can infect a healthy person [18, 20]. The superficial infections are called dermatophytosis, and they are commonly known as tinea or ringworm. Different forms of tinea affect different body areas. Tinea can affect the body (Tinea corporis), scalp (Tinea capitis), beard (Tinea barbae), hands (Tinea manus), feet (Tinea pedis), nail (Tinea unguium), or groyne and upper parts of the thigh (Tinea cruris). Individual species of three genera have been identified as the invading fungi in most forms of tinea: Microsporum, Epidermophyton, and Trychophyton. Intermediate fungal diseases invade both the superficial and deeper tissues; moniliasis caused by Candida albicans is an example. Deep fungal infections involve the epidermis, dermis, and subcutis. Infections that are typically superficial may exhibit deep involvement in immunosuppressed individuals [18, 20].

Viral Infections

It is reported that viruses invade the keratinocyte, begin to reproduce, and cause cellular proliferation or cellular death. The use of corticosteroid medications, which have immunosuppressive qualities, and birth control pills, which change the bacterial flora of the skin, has been linked to the sharp rise in viral skin illnesses [18]. Herpes simplex, Varicella (also known as chickenpox), Herpes zoster, Warts (Verrucae), Rubeola (Measles), and Rubella (also known as German measles) are some of the most common infectious skin disorders of viral origin [20].

Inflammatory and Allergic Skin Disorders

Inflammatory skin diseases are usually localized to the skin and are rarely associated with a specific internal disease. They produce marked variations in normal skin, usually papulosquamous in nature. Inflammation and erythema are common. Acne, lichen planus, psoriasis, and pityriasis resea are among the most common skin disorders of this type. Allergic skin responses involve the body’s immune system and are caused by hypersensitivity reactions. They include contact dermatitis, atopic and cummular eczema, and drug reactions [18, 20].

Use of Medicinal Plants on the Skin

Plants have been used for skin treatment since prehistoric times, with Egyptians recording skin care on temple wall paintings Grierson, et al. [21, 22]. About 33% of phototherapy in non-Western communities is used for skin disorders, wounds, and infections [23]. Topical application of medicinal plants has proven effective due to their biological activities, such as anti-microbial, anti-inflammatory, and anti-erythema properties [24].

It was confirmed that ethnobotanical surveys have been found to be one of the most reliable approaches to the bio- prospecting of medicinal plants and their uses. Many plant medicines have been incorporated into the mainstream of the healthcare system. The pharmaceutical industry has considered plant medicine as a source of bioactive agents that can be used in the preparation of medicine [25]. Effective and inexpensive botanical remedies are gaining popularity equally among both rural and urban areas [26].

Skin Diseases in Ethiopia

Although limited studies have been made on the prevalence of skin diseases in Ethiopia, the available records are indicative of the high prevalence of this problem in the country. A study made at Black Lion Hospital indicated that skin diseases are among the leading causes of hospital visits. The most common skin diseases were allergic skin diseases (25.5%), infections (25.4%), and photodermatoses (22.9%), followed by papulosquamous diseases (11.4%) and pruritus of unknown origin (3.3%). The pattern of skin diseases observed in this analysis shows that allergic and infectious causes account for three-quarters of skin problems [27]. It was also reported that of all the skin diseases that were diagnosed in 4,700 patients in one of the dermatological hospitals in the capital, dermatomycosis, vitiligo (including a group of genetically determined disorders characterised by an inability to produce melanin in the skin, hair, and eyes), and psoriasis accounted for 7.8%, 4.6%, and about 2%, respectively (Schaller, 1963, cited in Dawit, et al.). Another study conducted in 1980 involving 1, 000 patients showed skin disorders due to bacteria and fungi to be 12.7% and 9.7%, respectively, while psoriasis and vitiligo were 2.6% each [1].

A study made in northwest Ethiopia showed a prevalence rate of 49.2%. Tinea capitis, impetigo, infected wounds, and verrucae were the most common skin infections [28]. A related study made at Kazanchis Health Centre in Addis Ababa also reported that 15 bacterial, fungal, and viral infections were dominating, comprising 19.4%, 18.5%, and 6.5% of the Ncases [28].

In this review, a total of 233 plant species belonging to 170 genera and 71 families were found to be useful in the treatment of more than 24 different skin diseases like wounds, hemorrhoids, body swelling, ringworm, skin rush, itching, burns, aches, eczema, dandruff, boils, scabies, rashes, tinea versicularis, tinea nigri, and the like. Out of 233 plant species, 95 were invariably used for the treatment of wound diseases. Swelling, hemorrhoids, general skin diseases, skin rush, and dandruffs were treated consistently by 45, 35, 25, 24, and 22 species, respectively. The fewest (one or two) plant species treat diseases like leprosy, colic, mumps, meningitis, and so on. The review revealed that skin diseases, wounds, scabies, eczema, itching, ringworm, skin cancer (tumor), sores, skin eruptions, and swellings are very common among the different tribal communities of Ethiopia. The infection of the skin could be superficial, intermediate, or deep (Table 1; S1)

74 Datura stramonium L. Solanaceae Astenagir H L, Fr

75 Dichrostachys cinerea (L.) Wight & Arn. Fabaceae Gariggaruwa T L Wound 11

76 Delonix regia (Boj.ex Hook.) Raf. Fabaceae Mimi (Wol) T L Wound 17

77 Drymaria cordata (L.) Schultes Caryophyllaceae Sayidasajal H L Swelling, allergy, wound 1, 18

78 Discopodium penninervum Hochst. Solanaceae Almit S L Wound, dandruff 16

79 Dissotis senegambiensis (Guill. & Perr.) Triana Melastomataceae Kossosiya H R, L Fungal infection 11

80 Dodonaea angustifolia L.f. Sapindaceae Kitkita S L

81 Ehretia cymosa Thonn. Boraginaceae Ulaagaa T L Rheumatism 1

82 Embelia schimperi Vatke Myrsinaceae Enqoqo S Fl, L, sap Hemorrhoids, wound, itching, snake bite, 16,14

83 Erica arborea L. Ericaceae Asta S L Wound, 16

84 Eucalyptus globules Labill. Myrtaceae Bahir zaf T L Foot smell, skin diseases 1,3,9

85 Euphorbia abyssinica Gmel Euphorbiaceae Qulquql S St, lat Itching/scabies, wound, hemorrhoids 5, 7,16

86 Euphorbia ampliphylla Pax Euphorbiacea ‘Gineato’ S Sap Wound, hemorrhage, cancer 3, 18

87 Euphorbia colubrina Bally & Carter Euphorbiaceae Anterfa S Sap Ringworm 8

88 Euphoriba depauperata A. Rich. Euphorbiaceae Anxarfaa H Lat Eczema 12

89 Euphorbia lathryis L. Euphorbiaceae Hadaamii T St Hemorrhoids 2

90 Euphorbia platyphylos L. Euphorbiaceae Antir (Am) H Lat Tumor, wound, dandruff 3,6

91 Euphorbia schimperiana Scheele Euphorbiaceae Antirfa H Wp, sap Wound, skin disease 16,18

92 Euphorbia tirucalli L. Euphorbiaceae Shuramo (Wol) S Lat Skin cancer, hemorrhage, ringworm, wart

93 Falkia canescens C.H. Wright Convolvulaceae Gura hantutaa H L Spider poison, allergy 1

94 Ficus carica L. Moraceae Beles S Lat Wound 6,7

95 Ficus exasperata Vahl Moraceae Balansofi (Or) T Sap Warts, Eczema 4

Ring worm, dandruff, scabies head infection, hemorrhoids, head, wound

2, 3,4, 5, 6, 8,10,11, 16,17,13, 18,

Wounds, skin rush, eczema, Tinea versicolor, bone fracture, burn, skin rush

3, 5, 6, 8, 12, 16

4 ,8, 10, 15, 17,18

Table S1: List of Reviewed Medicinal Plants for Treating Skin Diseases.

Reviewed traditional medicinal plants in Ethiopia for the treatment of various skin diseases: Etana, 2010=1; Amenu, 2007=2 Abebe, 2011=3; Tolasa, 2007=4; Mesfin et al., 2014=5; Gebeyehu et al., 2014=6; Chekole, 2011= 7; Alemayehu, 2010=8; Yirga and Zeraburk, 2011=9 ; Mesfin et al., 2013=10; Agize, et al.,2013=11; Gebrehiwot, 2010= 12; Giday et al., 2007=13; Gidey et al., 2009=14; Megersa et al., 2013=15; Amsalu, 2010=16; Tamene, 2011)=17; Awas and Demissew, 2009=18. Key to Abbreviations: T-tree, S-shrub, H-herb, Cl-climber, L-leaf, R-root, Fl-flower, Wp-whole plant, Plant parts used- Pp, St-stem, Fr-fruit, Bar-bark, Lat-latex, Se-seed, R-root, Habit-Hb

Number of Reviewed Studies in Terms of Regions

In this review, a total of 18 districts (weredas) were taken from five regions (Amhara, Oromia, Benishangul-Gumuz, SNNPR, and Tigray). Amhara and Oromia account for five districts each, whereas SNNPRS, Tigray, and Benishangul- Gumuz, 4, 2, and 2 districts were selected, respectively (Figure 1; S2). However, the papers were taken randomly, and therefore the review does not indicate whether the given regions were extensively studied or not. In any case, the different research papers revealed that, compared to the huge number of districts in the country, the ethnomedicinal studies that have been undertaken are almost scanty. On the other hand, of the eighteen scientific papers taken into account from the five regions, nine of them are M.Sc. theses.

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Table S2: List of reviewed papers on ethnobotany.

Diversity of Medicinal Plants in Terms of Families

Asteraceae is the most dominant family, holding 19 plant species, followed by Fabaceae, which has 17 species. Other taxa commonly used are Solanaceae (15 spp.), Euphorbiaceae (14 spp.), Lamiaceae (11 spp.), Malvaceae (10 spp.), Ranunculaceae (7 spp.), Moraceae (6 spp.), Aloaceae, Anacardiaceae, Boraginaceae, Poaceae, and Rutaceae (5 each). The other fifty-eight families hold 109 species. Of which Acanthaceae, Capardiaceae, Commelinaceae, Convolvolaceae, and Cucurbitaceae each account for 4 species. The rest of the families signify one, two, or three species (Figure 2; S1).

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Different Parts of Plants Used to Cure Skin Diseases

The plant parts used ranged from leaves (90), root (29), root and leaf (19), latex/sap (18), seed (15), whole plant (9), stem (7), to barks and fruits (5 each). In addition, two or more combinations of parts (which account for 36), such as flowers, seeds, leaves, bark, latex, fruit, resin, rhizomes, and the like, were used. The survey data revealed that leaves were by far the most widely used plant parts, followed by roots, leaves, or roots in the preparation of remedies (see Fig. 3 and S1). The different reports in Ethiopia have also shown that leaves were the most commonly used, followed by roots, to treat various health problems [29, 30, 31].

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Habits of Medicinal Plants that Treat Skin Diseases

The review shows that the most widely used medicinal plants habit in the different study areas were herbs 101 (43%) followed by shrubs 74 (32%). Trees and climbers account 36 (16%) and 22 (9%) respectively (Figure 4; S1). Herbs are largest in number this may be due to the plant species exhibit high level of abundance and easy to access them. The results of this reviews agreed with the findings of other indigenous researchers including Berhanu, et al. [29, 32, 33, 34, 35, 36, 37]. On the contrary, the findings of Tamene B, et al. [13, 15, 30, 32, 36, 37] revealed that shrubs are the most commonly used habits in their respective different study sites of Ethiopia.

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Ten top Medicinal Plants used in the Prevention and Treatment of Skin Diseases

Based on the reviewed data from various sources, Croton macrostachyus and Dataura stramonium were cited by 12 authors as treating 6 and 7 skin diseases, respectively. Brucea antidysenterica, Plantago lanceolata, and Rhamnus prinoide were cited by 24 (each 8) authors and each of them treats 7, 7, and 6 dermatological diseases, respectively. Justicia schimperiana and Euphorbia tirucalli were the least both in terms of the number of diseases treated and the number of authors cited (Table 2). The diseases treated by the ten top medicinal plants were: skin lesion, dandruff, burn, open wound, skin infection boil, Tinea nigri, snake bite, ulcer, wound, itching, cut, eczema, skin disease, skin cancer, haemorrhage, ringworm, wart, open sore, rheumatism, scabies, herpes, blood clot, body swelling, poison, scabies, and athlete’s foot (Table 2; S1).

Preparations and Mode of Applications of Herbal Medicines

The majority of traditional medicinal plants were prepared using water as a medium. The mode of application was topical, confined to the affected portion of the skin [37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55]. In some cases, additives were added during applications. The above authors reported that the methods of preparation used by traditional healers were crushing, squeezing, and powdering. Most of the medicinal plants encountered in the study areas were prepared from a single plant or plant part. The use of multiple plants or plant parts for a single skin disease problem was rare. It was also reported that the condition of the plant materials used was fresh, dry, or fresh or dry.

Informant Consensus Factor (ICF) Related to Skin Disease Categories

The highest ICF (0.88) value is indicated in Tamen B, et al. [54] and the least one (0.67) is associated with Megersa M, et al. [52] (Table 3). However, the average ICF value is 0.78. The ethnobotanical reviews of “7” Weredas from different regions showed that the ICF values were obtained for diseases related to dermatological or skin problems (Table 2). This indicates that medicinal plants, which have higher ICF values, are assumed to be effective in treating a certain ailment. Some of the reported dermatological diseases with the highest value were wounds, skin swellings, haemorrhages, dandruff, and eczema (Table 2). Other authors, like Awas T, et al. [45, 55, 56], identified skin disease as the most commonly reported health problem in Kafficho people, Minjar-Shinkora, and Ofla districts, respectively.

Paired comparison, Preference ranking and direct matrix ranking of Medicinal

Plants used to Treat Skin Diseases

The paired comparison of five selected medicinal plants out of 15 species used to treat a disease called wound based on informant consensus showed that Euphorbia abyssinica, Ranunculus oligocarpus, Clematis simensis, Justicia schimperiana, and Dodonaea angustifolia stood 1st, 2nd, 3rd, 4th, and 5th, respectively [53]. For a similar disease, the same number of medicinal plants were identified and compared using ten informants to know their rank; thus, Plantago lanceolata stood first, followed by Rumex nepalensis Tolasa E, [41]. On the other hand, using seven informants Etana T, [57] found that Indigofera spicata species stood first for the treatment of skin allergies, and Drymaria cordata, Ipomoea tenuirostris, and Withania somnifera were ranked 2nd, 3rd, and 4th, respectively. Kalanchoe petitiana was the least preferred species to treat the disease in the area. He indicated that rank is because of the efficacy of the plant, at least in the context of local people.

The most preferred medicinal plants among the five species that were used to treat fibril illness in the study area, based on the responses of ten key informants, showed that Zehneria scabra ranked first, followed by Ocimum lamiifolium, and the least favoured one was Cyathula polycephala Gebrehiwot, [49]. Similarly, Abebe E, et al. [40], indicated that Zehneria scabra is the most preferred, while Cyathula polycephala is the least preferred of the other plant species cited in treating fibril illness.

Researchers also figured out the preference ranking of six medicinal plants that were reported for treating wounds after selecting ten key informants. Plantogo lanceolata ranked first, indicating that it is the most effective in treating wounds, followed by Rumex nervosus, and the least effective was Euphorbia platyphyllos [40]. Nicotiana tabacum stood first among the six plant species, followed by Senna didymobotrya, in treating snakebite [41]. By following the same method, it was also reported that Dodonaea angustifolia was rated as the most effective in treating wounds, followed by Solanium marginatum. This is based on the perceptions of ten traditional healers in the study area [49].

A direct matrix of randomly selected medicinal plants with different uses, including medicinal value, based on a given use criteria revealed that medicinal plants were broadly collected for different purposes such as charcoal, construction, fencing, firewood, forage, furniture, and the like Amsalu, et al. [49, 52, 53, 54, 57].