SKINCARE GUIDE: VITAMIN C

Vitamin C is a classic ingredient in cosmetics: the gold standard in antioxidant action, with countless benefits and used in almost all types of products, such as toners, moisturizers, eye creams and even sunscreens. Despite its notoriety and unshakeable reputation, there are some doubts and misconceptions about this essential ingredient.

Water-soluble, vitamin C is a natural component of healthy skin that the human being cannot produce, but which it receives and accumulates through food, particularly citrus fruits which justify the inevitable orange color chosen by the marketing departments from brands for most cosmetics rich in this ingredient.

It is the most abundant antioxidant in the skin, but as we age the skin becomes less able to store vitamin C from food or food complements, and its levels in the epidermis and dermis decrease. Fortunately, vitamin C cosmetics do exist and, when properly formulated and packaged, they work by helping to correct them.

At AVENUE CLINIC we believe that a personalized skincare routine is an important step on your well-being journey.

Vitamin C has many benefits for the skin: it is antioxidant, anti-inflammatory and anti-ageing. It protects the skin from environmental stress factors and pollution by neutralizing free radicals. Its anti-inflammatory action helps soothe irritated skin, particularly when exposed to the sun, and is very useful for acne-prone skin. As inflammation can compromise the skin barrier - impeding its ability to retain water - vitamin C also ensures more hydrated and softer skin. It also increases collagen production, which results in firmer, less wrinkled and younger-looking skin. It regulates the production of melanin, due to its action on the enzyme tyrosinase, reducing dark spot and illuminating complexion. Vitamin C also boosts the antioxidant capacity of other molecules naturally present in the skin or in cosmetics, such as vitamin E, coenzyme Q10 and ferulic acid.

  • Vitamin C is used in cosmetics in two main forms: the first is ascorbic acid, or pure vitamin C - L-ascorbic acid - and the second is ascorbyl glucoside, or vitamin Cg, which is more stable and, from the outset, better tolerated by sensitive skin.
    Ascorbic acid is the most effective form of vitamin C and the most biologically active, but this molecule has some difficulty penetrating the skin because it is hydrophilic and is therefore formulated at a more acidic pH than usual, below 3.5. As less sensitizing alternatives, some derivatives have been synthesized, such as sodium ascorbyl phosphate, magnesium ascorbyl phosphate or ascorbyl palmitate, which are stable at acidic but higher pH.

  • Concentrations in cosmetics can vary, but between 5% and 15% is considered ideal, with up to 20% being relatively common. More than this concentration can cause some discomfort, limiting its regular use by most skins. Below 5%, it has been proven that it continues to have an effect and helps to preserve other ingredients in the formulations, such as retinol or ceramides.

  • Cosmetics with vitamin C can be used twice a day, morning and night. If we have to choose just one time, the ideal moment is in the morning, so that we can benefit from its antioxidant power at the time of day when we need it most, always followed by a sunscreen with SPF 30 or higher. In fact, topical vitamin C has been shown to be a second line of defense against harmful UVA rays, also helping to strengthen the antioxidant defenses of sun-exposed skin. Vitamin C is not photosensitizing.

  • All forms of vitamin C are easily combined with other ingredients, including niacinamide, retinoids and exfoliating acids. The myth that you can't mix it with niacinamide comes from old studies dating back to the 60s. Today, it is known that it is safe to mix niacinamide with vitamin C, either through the same product, or combined from different products overlapping in the same use. These ingredients offer distinct but synergistic benefits.The undesirable by-product of niacinamide with vitamin C - nicotinic acid - only becomes a problem when niacinamide and vitamin C are combined in a high-temperature environment for a long time, a higher temperature than is found in most domestic environments. Furthermore, it's important to note that this concern only applies to pure vitamin C, not its many other forms. There are several products on the market that combine the two vitamins in complete safety.

  • Vitamin C is suitable for all skin types. From a sensitivity point of view, it can be used by everyone. For more sensitive skin, it is recommend to use lower percentages, around 5%-10%, or glycosylated vitamin C, which doesn't require such an acidic formula pH. Very sensitive skin can be tested for allergies on the back of the ear before starting to use the product all over the face.

  • Pure vitamin C is unstable, photosensitive and degrades very easily in the presence of oxygen or in contact with sunlight or very strong artificial light, becoming inactive in cosmetics. Its oxidation is often visible through the darkening of the product's texture. It is preferable to opt for opaque, dark packaging that minimizes light permeation. There are several options on the market: tubes, dosage bottles and even single-dose ampoules. These types of packaging will be a safer choice in terms of preserving the product. It is also important to gently screw or close the packaging so as not to introduce oxygen into the formula.

  • High temperatures accelerate its decomposition, so if there's one ingredient that should be kept in the fridge, it's vitamin C. In the absence of a specific fridge for cosmetics, you should always prefer a dark, cool and dry place, away from light and sources of excessive heat.

By Joana Nobre, pharmacist cosmetologist, for AVENUE CLINIC

Avenue Clinic