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Hair and hairy scalp
Published in Richard Ashton, Barbara Leppard, Differential Diagnosis in Dermatology, 2021
Richard Ashton, Barbara Leppard
Hair is a modified type of keratin produced by the hair matrix (equivalent to epidermis). On the scalp, apart from its social and cosmetic function, hair protects the underlying skin from sun damage.
An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
The hair shaft grows from highly active, modified epidermal tissue known as the hair matrix. The shaft traverses the hair follicle canal, which is made up of a series of investing epidermal sheaths, the most prominent of which is the external root sheath (Figure 1.5). The whole follicular structure is nourished by a small, indenting cellular and vascular connective tissue papilla, which pokes into the base of the matrix. The sebaceous gland secretes into the hair canal a lipid-rich substance known as sebum, whose function is to lubricate the hair. Sebum contains triglycerides, cholesterol esters, wax esters, and squalene. Hair growth and sebum secretion are mainly under the control of androgens, although other physiological variables may also influence these functions.
Comparative Anatomy, Physiology, and Biochemistry of Mammalian Skin
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The hair follicle is composed of three primary layers: inner root sheath, outer root sheath, and connective tissue sheath. The first is composed of scale-like keratinized cells which interlock with cuticle cells of the hair. The second is continuous with the epidermis. Structurally, it resembles epidermis but also has glycogen in it. The third layer, the connective tissue sheath layer, is continuous with the papillary layer of the dermis and with the dermal papilla of the hair follicle. At the base of the hair follicle, termed the bulb, the dermal papilla and hair matrix are located. The matrix is composed of the germinative epithelial cells which give rise to the hair proper, and is the region responsible for biochemical regulation of hair growth. They are also the target cells for toxicants directly affecting hair growth.
In vivo percutaneous permeation of gold nanomaterials in consumer cosmetics: implication in dermal safety assessment of consumer nanoproducts
Published in Nanotoxicology, 2021
Mingjing Cao, Bai Li, Mengyu Guo, Ying Liu, Lili Zhang, Yaling Wang, Bin Hu, Jiayang Li, Duncan S. Sutherland, Liming Wang, Chunying Chen
As revealed by the HE staining, the hair bulb was damaged after dermal exposure to the cosmetic creams and the extracted gold nanosheets (Figure 5(A,E)). The hair bulb is a key structure for the growth of hair since the hair matrix and dermal papilla are located. Three proteins, ALP, CD34, and KRT19, detected in IHC are the indicators of hair growth. ALP protein in the dermal papilla can be activated in the hair growth cycle. CD34 protein is the marker of hair follicle stem cells playing a vital role in hair growth. KRT19 is the structural protein of the hair shaft. The down-regulation of the three protein expressions suggested the hair growth could be inhibited by the cosmetic creams containing Au nanosheets (Figure 5(B–D,F)). Hair removal is popular in the beauty industry. The cosmetic cream containing Au nanosheets might have the potential to act as a beauty product for hair removal.
Site-specific drug delivery in the skin for the localized treatment of skin diseases
Published in Expert Opinion on Drug Delivery, 2019
Yang Chen, Xun Feng, Shengnan Meng
Within the pilosebaceous unit, there are several targets that are of interest in the treatment of dermatological abnormalities, especially those related to the hair follicle, such as acne, androgenetic alopecia, alopecia areate, and some skin cancers [42]. These targets include the sebaceous gland, hair follicle papilla, hair matrix, and specific cell populations in and around the hair follicles, such as the stem cells in the bulge region and immunocompetent cells in the infundibulum [7,39]. Targeting hair follicle offers opportunities for localized delivery in hair growth disorders including alopecia and hypertrichosis, while targeting the sebaceous glands may be helpful for the treatment of sebaceous gland-related dysfunctions such as acne, seborrhoeic eczema, and rosacea [45,46]. In addition, the stem cells in the bulge region provide the target for gene delivery to facilitate long-term gene correction of congenital hair disease or genetic skin disorders [7,8,47]. The peri-follicular antigen presenting cells enables transfollicular antigen delivery which is an attractive new avenue for needle-free immunization [48]. The sebum secreted from sebaceous glands creates an environment enriched in neutral and nonpolar lipids, and hence, the sebaceous glands offer a potential pathway for the uptake of some lipophilic molecules but may also impede penetration of hydrophilic drugs [38].
Long-term outcome of a patient with paradoxical hypertrichosis after laser epilation
Published in Journal of Cosmetic and Laser Therapy, 2018
Adam Honeybrook, Tascha Crossing, Eric Bernstein, Jason Bloom, Julie Woodward
Another factor that has not been well explored in relation to paradoxical hair growth is treatment interval length. Hair growth models suggest the follicle germinative epidermal cells reside in the so-called bulge area of the follicle. These cells form the new hair matrix to initiate the growth, anagen, phase during the conclusion of the telogen phase. Theoretically, it is during this rapidly dividing period that the hair follicle is most sensitive to the thermal effects imparted from a laser or other light source (20). Therefore, the ideal treatment interval seems to be as soon as hair regrowth occurs, which varies by anatomic location (Table 1) (21). However, this theory has never been confirmed, and hence the reason for considerable variation between practitioners when recommending intervals between treatment sessions. Schroeter and colleagues determined that most cases of terminal hair growth in their study occurred when treatment intervals were more than 8 weeks apart. As a result, they advise that the interval between treatments be between 4 and 6 weeks (22). In 2000, Lloyd et al. performed a study of 11 patients who received five treatments at 3-week intervals to the right groin using an Alexandrite laser and reported “excellent” results with 78% clearance of hair noted at 1 year (23). These findings suggest that the treatment interval of 10–12 weeks in our case may have been a predisposing factor for the development of paradoxical hypertrichosis and decreasing the amount of time between treatments may reduce the risk of this complication.