Oxidative Stress and Ageing Well
A major cause of ageing is oxidative stress. It is really important to understand what causes oxidative stress and how we can prevent it. Not just for our skin, but for the health of our body as well.

Damage to the DNA, proteins, and lipids is caused by oxidants (highly reactive substances). We produce these as a normal part of our biological processes and happens when we breath, but also from infections, inflammation and the consumption of cigarettes, alcohol and other pollutants.
Skin acts as an external barrier so it is directly exposed to environmental stress, such as pollutants and sunlight. The sun's UVA radiation generates free radicals in the skin, when there is excessive exposure the natural defence systems are overwhelmed and oxidative damage occurs.
To understand what Free Radicals are you need to read a bit of science, here is a basic description from Medical News today:
"Atoms are surrounded by electrons that orbit the atom in layers called shells. Each shell needs to be filled by a set number of electrons. When a shell is full; electrons begin filling the next shell.
If an atom has an outer shell that is not full, it may bond with another atom, using the electrons to complete its outer shell. These types of atoms are known as free radicals.
Atoms with a full outer shell are stable, but free radicals are unstable and in an effort to make up the number of electrons in their outer shell, they react quickly with other substances.
When oxygen molecules split into single atoms that have unpaired electrons, they become unstable free radicals that seek other atoms or molecules to bond to. If this continues to happen, it begins a process called oxidative stress.
Oxidative stress can damage the body’s cells, leading to a range of diseases and causes symptoms of ageing, such as wrinkles.

Antioxidants are chemicals that lessen or prevent the effects of free radicals. They donate an electron to free radicals, thereby reducing their reactivity. What makes antioxidants unique is that they can donate an electron without becoming reactive free radicals themselves.

No single antioxidant can combat the effects of every free radical. Just as free radicals have different effects in different areas of the body, every antioxidant behaves differently due to its chemical properties.
Antioxidant Nutrients
Vitamin C: Broccoli, Brussels sprouts, cantaloupe, cauliflower, grapefruit, leafy greens (turnip, mustard, beet, collards), honeydew, kale, kiwi, lemon, orange, papaya, snow peas, strawberries, sweet potato, tomatoes, and bell peppers (all colours)
Vitamin E: Almonds, avocado, Swiss chard, leafy greens (beet, mustard, turnip), peanuts, red peppers, spinach (boiled), and sunflower seeds
Carotenoids including beta-carotene and lycopene: Apricots, asparagus, beets, broccoli, cantaloupe, carrots, bell peppers, kale, mangos, turnip and collard greens, oranges, peaches, pink grapefruit, pumpkin, winter squash, spinach, sweet potato, tangerines, tomatoes, and watermelon
Selenium: Brazil nuts, fish, shellfish, beef, poultry, barley, brown rice
Zinc: Beef, poultry, oysters, shrimp, sesame seeds, pumpkin seeds, chickpeas, lentils, cashews, fortified cereals
Phenolic compounds: Quercetin (apples, red wine, onions), catechins (tea, cocoa, berries), resveratrol (red and white wine, grapes, peanuts, berries), coumaric acid (spices, berries), anthocyanins (blueberries, strawberries)
As the body ages, it loses its ability to fight the effects of free radicals. The result is more free radicals, more oxidative stress, and more damage to cells, which leads to degenerative processes, as well as “normal” ageing.
References
https://www.medicalnewstoday.com/articles/318652#What-are-free-radicals