Introduction

Over the past 10 to 15 years, men have been placing a greater emphasis on aesthetic appearance as traditional gender roles have evolved. The emergence of the metrosexual male exemplifies this evolution. ¹ Male skincare products and cosmetic procedures have become increasingly popular as men represent a growing segment of the cosmetic industry. In 2012, over 90% of U.S. men older than 18 years reported use of some type of grooming product. ² In 2010, Euromonitor International reported that the global male grooming market reached over $29 billion. ³ Shaving and deodorant products made up the majority of grooming products in this report, yet men’s hair care and skincare products still accounted for a significant proportion of sales. From 2010 to 2011, the U.S. male grooming market sales grew 11%, further attesting to the rising popularity of male aesthetics. Additionally, men are increasingly undergoing cosmetic medical procedures, including hair transplantation, rhinoplasty, eyelid surgery, scar revision, and facelift. ⁴ This chapter seeks to elucidate gender differences in cutaneous physiology and offer insightful clinical pearls relevant to male skincare based on these differences.

Cutaneous Physiology

Despite similar structure and function, human skin has several notable gender-specific differences. Some of these differences are related to hormonal differences between males and females. Estrogens, the predominant female hormones, play a role in regulating the epidermis. ¹ On the other hand, androgens, the predominant male hormone, regulate the dermis, as well as hair shaft thickness.

Skin thickness certainly differs between genders. Skin collagen, used as a marker for dermal thickness, is more abundant in males compared to females at all ages. ⁵ Additionally, while male skin collagen content decreases steadily throughout life, female skin collagen content remains stable until the fifth decade of life, during which there is a significant decrease. The abrupt decrease in skin collagen content perimenopausally suggests that estrogen may play a protective role in maintaining skin thickness in females, which is lost as estrogen becomes depleted during menopause. Males have also been shown to have a significantly thicker cellular epidermis compared to females. ⁶ However, magnetic resonance imaging has helped demonstrate that females have thicker subcutaneous adipose tissue compared to their male counterparts. ⁷

Males and females also differ in both terminal hair production and distribution. The growth of sexual hair is dependent on androgens. Androgen-dependent regions include the chin, upper lip, chest, breasts, abdomen, back, and anterior thighs. Male beards rely on testosterone for continued growth. In one study, male transsexual patients received superactive luteinizing hormone–releasing hormone analogue to decrease plasma testosterone and dihydrotestosterone levels, which effectively reduced beard hair growth. ⁸ Additionally, masculinizing disorders in females, such as congenital adrenal hyperplasia and polycystic ovarian syndrome, lead to hirsutism as a result of increased circulating androgens, highlighting the relationship between androgens and hair growth. ⁹

In addition to differences in terminal hair production and distribution, males tend to experience greater sebaceous gland output. Sebaceous glands are holocrine glands, generally associated with hair follicles, which produce sebum. The growth and activity of sebaceous glands are dependent on androgen stimulation. ¹⁰ Therefore, males tend to have more facial sebum production. ¹¹ In males, peak sebum production occurs between 15 and 35 years old and declines thereafter. Sebum serves to provide the stratum corneum with a hydrophobic layer; however, excess sebum can lead to acne and unfavorable aesthetics such as oily-appearing skin.

Additionally, males tend to have greater sweat rates compared to females (800 vs. 450 cc/hour during exercise). ¹² Since sweat is a product of both eccrine and apocrine glands, these glands may be more active in males.

Given these differences in the amount of sebum and sweat present on male skin versus female skin, it is plausible that there is also a difference in skin surface pH. A study of a Chinese population conducted in San Francisco found females to exhibit a higher skin pH compared to males. ¹¹ In particular, facial skin pH in multiple facial zones has been shown to be lower in males. ¹³ It is unclear whether this physiological difference in pH has clinical value. However, it is possible that skin pH may be indicative of subtle differences in cutaneous bacterial flora, barrier function, and tolerability of cosmetic products.

Skin Aging

There are gender differences in the process of skin aging as well. As a result of both intrinsic and extrinsic factors, women tend to age more favorably than men. In one European cross-sectional study, men appeared 0.37 years older than their age, whereas women appeared 0.54 years younger. ¹⁴ More studies need to be performed to evaluate skin aging in other ethnic populations.

Rhytids, or wrinkles, are a major sign of skin aging that develop from a combination of mechanical stress, ultraviolet radiation (UVR), and oxidative stress. ¹⁵ Repeated muscle contractions, such as in facial expressive movements, contribute to mechanical stress. UVR from sun exposure leads to the degradation of elastic fibers that normally function to oppose this mechanical stress.

Rhytids develop earlier, tend to be deeper, and are more numerous in men because of differences in facial musculature and sun-protective behavior. ¹⁶ However, in the 65- to 75-year-old age range, wrinkles in women were noted to be greater than or equal to those in men, suggesting that estrogens may play a protective role against wrinkles in premenopausal women. This clinical finding may be related to the aforementioned loss of skin collagen content that women experience perimenopausally. The dramatic loss of skin collagen content that coincides with decreased estrogens during the menopausal transition is likely a predisposing factor for the development of rhytids in women of this age group.

Deep rhytids most commonly affect the forehead in males and the perioral area in females. ^{17 , 18} Men have been noted to have a “U-shaped” glabellar wrinkle pattern caused by the contraction of the procerus and corrugator muscles. ¹⁹ Nasal wrinkles were also noted to be more common in males. Additionally, men more commonly exhibited the lower fan crow’s feet pattern. ²⁰ Understanding these gender differences in wrinkle patterns may help guide future treatment options.

Facial volume loss may lead to the formation of rhytids, jowls, and hollowing. Although both genders are affected, males tend to experience gradual soft-tissue atrophy of all anatomical areas, whereas females experience more dramatic soft-tissue atrophy between 30 and 60 years. ^{21 , 22}

The periorbital area is also an important aesthetic unit. Because of anatomical differences, aging males tend to experience greater periocular and lower eyelid changes compared to females, such as more severe lower eyelid sagging and increased lower eyelid prominence. ¹⁵ These findings are likely a result of a combination of decreased dermal elasticity and changes in skeletal structure with male aging. ²³ In general, although upper eyelid sagging is more common in females, males are at greater risk of severe sagging. ²⁴ Anatomically, the inferomedial quadrant of the male orbit is more likely to recede over time. This phenomenon likely plays a role in accentuating age-related changes of the male periorbital aesthetic unit.

Sun Protection for Men

Skin cancer is the most common cancer in the United States and is estimated to affect one in five Americans at some point in their lifetime. ^{25 , 26} Nonmelanoma skin cancers (NMSCs), such as squamous cell carcinoma and basal cell carcinoma, represent the majority of skin cancers. The incidence of melanoma doubled from 1982 to 2011, and according to the American Cancer Society, invasive melanoma is projected to be the fifth most common cancer in men (52,170 cases) in 2017, compared to 34,940 cases in women.27 Men also have double the risk of developing NMSC compared to women. ²⁸ Skin cancer treatment costs are estimated to be $8.1 billion annually, and while fortunately skin cancer is preventable, greater educational campaigns and preventative screening programs are needed to reduce its rising incidence. ²⁹

In the United States, men and women are at a significant risk of developing skin cancer because of inadequate sun protection. In 2010, less than onehalf of U.S. adults reported applying sunscreen 15 sun-protective factor (SPF) or higher (31%), wearing sun-protective clothing (40%), or seeking shade (37%) when outdoors. ³⁰ Adult men exhibit especially poor sun-protective behavior. About 67% of adult men use one or more of the aforementioned methods of sun protection compared with 73% of adult women. Additionally, less than 15% of men use sunscreen on their face and other sun-exposed areas of skin compared to 30% in women. This clear disparity in basic sun-protective behavior is supported by studies that show that adult men experience higher rates of sunburn compared to adult women. ³¹

Physiologically, males may be at an increased risk for developing skin cancer compared to females. Several studies show that men have higher circulating levels of markers of oxidative stress compared to females. ³² These markers include F2-isoprostanes and thiobarbituric acid–reactive substances, both of which are indicative of the presence of reactive oxygen species (ROS) in humans. ^{33 , 34} Higher levels of ROS in males may be a result of multiple factors, including a higher metabolic rate and the relative lack of estrogen, which may serve as an antioxidant in females. ^{35 , 36}

Furthermore, males exhibit greater UVR-induced immunosuppression compared to females. According to an Australian study, suberythemal solar-stimulated UVR caused significant immunosuppression, measured as Mantoux response, in both males and females. In this study, however, males experienced immunosuppression at three times lower UVR dose compared to females. ³⁷ Therefore, sun protection may play an even more important role in males. This study also demonstrated that topical nicotinamide played a role in preventing immunosuppression, suggesting the potential utility of this vitamin in the prevention of skin cancer.