Find out which cosmetic ingredients should not be combined, particularly during the summer months, to help keep your skin healthy, protected and in good condition.
The rise in temperatures at the beginning of summer means that some adjustments to skincare and cosmetic routines may be advisable in order to reduce the risk of adverse reactions such as dermatitis, flare-ups, worsening of existing skin conditions or pigmentation changes.
Warmer weather alone may make lighter cosmetic textures more comfortable on the skin. However, temperature is not the only factor to consider: sun exposure can also trigger adverse reactions when certain active ingredients are present on the skin.
Dermatologists at Grupo Pedro Jaén and Paula Jaén, Head of the Beauty and Wellbeing Unit and our pharmacy, explain which cosmetic products and ingredients require particular care when sun exposure is more intense.
Take care with perfume in summer
It is common to be cautious about using perfume in summer. Sweat and heat can alter fragrances and change their final scent. From a dermatological perspective, however, the main concern is that some perfumes may contain substances such as bergamot or lime extracts.
As Paula Jaén explains, “perfumes can contain substances that react when exposed to sunlight and may cause irritation, pigmentation changes and even mild burns in more sensitive skin.” These include alcohol and certain fragrance fixatives used to make the scent last longer, such as bergamot essence and musk.
Some of these substances can cause Berloque dermatitis, a phototoxic reaction triggered by ultraviolet radiation. It is characterised by pigmentation changes in areas where perfume has been applied and which are subsequently exposed to sunlight. In people with very fair skin, these reactions may initially appear reddish and can sometimes be accompanied by blistering. In darker phototypes, the pigmentation may be more brownish and vary in intensity.
Although this is not generally a serious condition, the resulting hyperpigmentation can persist for months and, in some cases, may not disappear completely.
Other plants not used in perfume manufacture can cause similar reactions after skin contact. Examples include celery and fig plants. As discussed elsewhere on this blog, Berloque-type dermatitis associated with preparing mojitos may occur after handling lime. The compounds present in this citrus fruit can contribute to itching, redness or blistering after subsequent sun exposure.
Does this mean perfume should be avoided completely during summer? Not necessarily. It is generally sufficient to avoid applying perfume to sun-exposed skin before going outdoors. If necessary, areas such as the neck, wrists or décolletage can be washed before prolonged sun exposure.
Can vitamin C be used in summer?
Vitamin C is one of the most widely used antioxidants in skincare. It helps counteract free radicals generated through cellular metabolism and environmental exposure, which contribute to skin ageing and photoageing.
There is a common misconception that vitamin C should not be used during summer because it can cause pigmentation. However, modern formulations can be stable and compatible with sun exposure. Vitamin C may also contribute to antioxidant photoprotection. This does not replace the need for daily sunscreen.
The same applies to formulations combining vitamin C with other ingredients such as vitamin E and ferulic acid, which can enhance antioxidant activity and improve formulation stability. These products should be applied before sunscreen as part of a morning skincare routine.
Should retinol and acids be stopped in summer?
Retinol is a vitamin A derivative used in many cosmetic formulations because of its effects on signs of skin ageing, including wrinkles, pigmentation and skin texture. Depending on its concentration, it may cause mild exfoliation or more noticeable peeling. For this reason, it is advisable to use it under dermatological guidance, particularly when retinol is combined with other exfoliating acids commonly used in skincare, such as glycolic, tartaric, malic, salicylic, citric or lactic acid.
The acids used in cosmetic skincare are not necessarily photosensitising in themselves. However, many work by increasing cell turnover and exfoliating the skin surface. Some products contain two or more acids, and their effects may be cumulative. This can leave the skin more sensitive and therefore more vulnerable to ultraviolet radiation, increasing the risk of irritation, sunburn and pigmentation changes.
For this reason, when using retinol or exfoliating acids during the summer, it is important to reinforce sun protection and follow the recommendations of a dermatologist. Depending on the individual case, the dermatologist may advise reducing the concentration of active ingredients, modifying combinations or spacing applications — for example, using the product on alternate days rather than daily.
Cosmetic ingredients you should not mix throughout the year
Vitamin C and niacinamide
Niacinamide is a form of vitamin B3 with several recognised benefits when applied topically. It helps support the skin barrier and hydration, contributes to skin regeneration and has anti-inflammatory and antioxidant properties. Our specialists recommend it to help improve skin texture, smooth the skin surface, reduce the appearance of acne marks and regulate pigmentation.
At an acidic pH, niacinamide may convert into niacin, or nicotinic acid, which can cause skin irritation. Some vitamin C products are formulated at a low pH. For this reason, the original article recommends avoiding layering these two active ingredients in the same routine and instead using vitamin C during the day and niacinamide at night.
Vitamin C and alpha hydroxy acids (AHAs)
Another example of cosmetic ingredients that the original article advises against combining in the same routine is vitamin C and alpha hydroxy acids. Both can be potent active ingredients, and using them together may increase the risk of irritation and excessive peeling in some skin types.
Vitamin C and benzoyl peroxide
Benzoyl peroxide is commonly used in the treatment of acne because of its antibacterial and anti-inflammatory effects. It can cause dryness, sensitivity and irritation as side effects. Because benzoyl peroxide acts through an oxidative mechanism, combining it with certain antioxidant formulations may reduce the effectiveness of one or both products. For this reason, it may be preferable to use them separately.
Retinol and benzoyl peroxide
As mentioned above, benzoyl peroxide can cause skin dryness, so its use is often accompanied by appropriate moisturising products. Combining retinol and benzoyl peroxide may increase irritation because both ingredients can be poorly tolerated when used together in some patients. There are prescription acne treatments that combine benzoyl peroxide with specific retinoid derivatives, although these are medical formulations and are not the same as combining cosmetic retinol with benzoyl peroxide independently.
When both ingredients are required, the original article recommends using benzoyl peroxide during the day and retinol at night. If a specialist considers that benzoyl peroxide should be applied both morning and evening, appropriate moisturisation and a broad-spectrum SPF 50+ sunscreen should be used during the day.
Post updated. First version published on 26 July 2022.
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