As people age, skin loses its youthful firmness and regenerative capacity when it was once plump and smooth during its prime, exuding health. However, as time passes, there's a noticeable decline in firmness, resulting in sagging, dullness, and wrinkles. But what specifically causes this?
Understanding Skin Aging: What Causes Wrinkles and Why Do Old People Have Them?
Wrinkles Form As People Age
The skin comprises three layers: the epidermis, dermis, and hypodermis. The epidermis, the outermost layer, offers the initial protective barrier against damage and infection.
The dermis, the second layer, contains various components such as connective tissue, hair follicles, blood vessels, lymphatic vessels, and sweat glands. Lastly, the hypodermis, the deepest layer, consists primarily of fat and additional connective tissue.
The face, being the most exposed area of human skin, is susceptible to wrinkles, a culmination of factors. Intrinsic changes lead to thinner, weaker, and less elastic skin, coupled with a decline in supporting muscle, bone, and fat.
Extrinsic aging accelerates tissue degradation due to factors like sun damage, smoking, diet, and pollution. Physical expressions, such as smiling and frowning, contribute to line formation, with these lines becoming permanent as skin ages.
The onset of wrinkles can begin in one's 20s, often manifesting as horizontal lines when raising the eyebrows. In one's 30s, additional lines may appear, such as crows' feet around the eyes, influenced by sun exposure and squinting.
The 40s and 50s bring more visible lines under the eyes and around the mouth, while deeper wrinkles may emerge. In one's 60s and beyond, wrinkles can become extensive, with the most prominent ones exceeding 2mm in depth. These lines can also result from consistent facial pressure when sleeping in the same position.
Beyond its physical protection role, the skin serves as a frontier for the immune system. It is populated by various immune cells like macrophages, monocytes, B cells, and T cells, ready to respond to potential damage or infection. Salvador Aznar Benitah and his team investigated age-related changes in skin immune cells to understand potential decreases in cell numbers and activity.
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What Causes Wrinkles?
Researchers at the Barcelona Institute of Science and Technology have identified interleukin-17 (IL-17), a signaling protein, as a potential key mechanism driving the aging process. Their study, published in Nature Aging, utilized single-cell RNA sequencing to analyze thousands of individual skin cells from old and young mice, shedding light on age-related cellular changes.
When comparing nonimmune skin cells from old and young mice, researchers found subtle differences, with a slight increase in global inflammation in aged skin. However, a more significant deviation was observed in immune cells. In aged skin, the myeloid lineage of immune cells, responsible for the early immune response, was significantly more active and showed signs of chronic inflammation.
The lymphoid lineage, associated with the adaptive immune system, was also overactive, particularly in specific T cells and innate lymphoid cells. These cells, which usually coordinate immune defenses, became more active in old skin despite the absence of clear damage or threats.
The increased inflammation in aged skin was primarily driven by IL-17, a family of signaling proteins. Certain immune cells in old mouse skin were secreting IL-17A and IL-17F, leading to heightened inflammation. IL-17A is well-known for its association with various inflammatory autoimmune diseases, including skin conditions like psoriasis.
Overall, this research provides insights into the role of IL-17 in skin aging and inflammation, potentially opening avenues for interventions to slow or prevent skin aging.
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