Skin aging occurs through two primary processes: intrinsic aging and extrinsic aging. Intrinsic aging is influenced by chronological and genetic factors—essentially, the natural passage of time and inherited traits. In contrast, extrinsic aging results from environmental and lifestyle factors, such as sun exposure and smoking.

When examined under a microscope, intrinsically and extrinsically aged skin show distinct differences. These microscopic structural changes are reflected in their visible appearance to the naked eye. Intrinsically aged skin appears thinner and finely wrinkled, while extrinsically aged skin has a coarse, leathery texture with deeper wrinkles.

The photograph referenced, originally published in the New England Journal of Medicine, illustrates this contrast vividly. It features a 66-year-old truck driver whose left side of the face experienced prolonged sun exposure through his truck window over 28 years. The right side, affected only by intrinsic aging, is markedly different from the sun-damaged, extrinsically aged left side. This type of damage is referred to as photoaging.

What Can Be Done?

While the natural aging process cannot currently be reversed, many of the external factors that contribute to visible skin aging can be reduced or prevented.

Sun Exposure and Skin Aging

One of the most significant causes of premature skin aging is exposure to ultraviolet (UV) radiation from the sun. Sunlight emits two main types of UV rays that affect the skin differently:

• UVB rays primarily affect the outer layers of the skin and are responsible for sunburn.
• UVA rays penetrate more deeply and play a major role in photoaging, including wrinkles, pigmentation changes, and loss of skin elasticity.

Protecting the skin from UV exposure is one of the most effective ways to maintain long-term skin health and appearance.

Using Sunscreen Effectively

A broad-spectrum sunscreen, which protects against both UVA and UVB rays, is recommended for daily use. For optimal protection:

• Apply sunscreen approximately 15 minutes before sun exposure.
• Reapply every two hours when outdoors.
• Reapply after swimming, sweating, or rubbing the skin with a towel.

It is also important to remember that UV exposure occurs even on cloudy days. UV rays can pass through clouds and reflect off surfaces such as water, sand, and concrete. In addition, UVA rays can penetrate glass, meaning exposure may still occur indoors near windows or while driving.

Consistent sun protection is therefore an important part of preventing premature skin aging and reducing long-term skin damage.

The Role of Retinoids in Photoaging

Retinoids are among the most effective topical treatments for improving signs of photoaging. These vitamin A derivatives increase skin cell turnover and stimulate collagen production, helping to reduce fine lines, uneven pigmentation, rough texture, and loss of skin elasticity caused by chronic sun exposure.

Among retinoids, tretinoin is considered the most potent and well-studied option. Available by prescription in many countries, tretinoin has substantial clinical evidence supporting its ability to improve photoaged skin over time. Compared with over-the-counter retinol, tretinoin works more directly within the skin and typically produces more noticeable results, particularly for wrinkles, pigmentation, and skin texture.

Over-the-counter retinol products can still provide benefit, especially for individuals with sensitive skin or those new to retinoids, but their effects are generally milder and may take longer to become visible.

Because retinoids can initially cause dryness, redness, peeling, or irritation, they are usually introduced gradually. Daily sunscreen use is essential while using retinoids, as the skin may become more sensitive to sun exposure during treatment.