What's the difference between lips and skin? In this installment of our "Comparatively Speaking" series, Tony O'Lenick asked Apostolos Pappas, Ph.D., of Johnson & Johnson, to explain. Here, Pappas provides insight on differences in physiology and function—interesting points to consider when considering or developing skin or lip care products.
"Lips constitute the visible and frontal part of the mouth and oral cavity. They are softer and more movable than skin, and are the entry point for everything that has taste and aroma. The lips can also alter the articulation of speech and the melody of sound, playing a pivotal role in whistling or playing a wind instrument.
"The juncture where the lips meet the surrounding skin of the mouth area is known as the vermilion border. The typically reddish area within this border is the vermilion zone. Its color is due to the presence of eleidin, a clear intracellular protein, through which blood vessels near the surface of the papillary layer are visible, revealing a "red blood cell" color.
"Both skin and lips offer sensory feedback via nerve endings but the epithelium in lips is far thinner than the highly keratinized external epidermis of skin. The lips have only three to five cellular layers, compared with the average 15-20 layers in skin. They also contain fewer melanocytes; therefore any melanin produced does not interfere substantially with the red color of lips.
"Sebaceous and sweat glands as well as hair follicles stop adjacent to the borders of lips, in contrast to skin. Due to the absence of defense glands and more keratinized layers, the lips are more susceptible than skin to pathogens, drying conditions and extreme temperature fluctuations. Thus, lips dry out faster, become chapped easier and can manifest viral infections."