Skin Microbiome and the Sea: What Happens to Your Skin in Seawater?

"Seawater is rich in minerals and trace elements such as sodium chloride, magnesium, iodine, and potassium. From a chemical perspective, its composition is remarkably similar to that of the biological fluids naturally found within our cells, including blood plasma. This similarity allows the skin to tolerate and absorb these minerals through biochemical exchange. When we immerse ourselves in seawater, several physical and chemical processes take place simultaneously:

• Osmotic action and mechanical cleansing. Saltwater mechanically removes dead skin cells, excess sebum, and some surface impurities, providing a gentle cleansing effect.
• pH modulation. Healthy skin has a slightly acidic pH, typically between 4.7 and 5.5, which is essential for supporting beneficial bacteria while preventing the growth of harmful microorganisms. Seawater, by contrast, is more alkaline, with a pH close to 8. This temporary shift alters the skin's environment, briefly slowing the growth of some resident microbes and prompting the microbiome to rebalance itself once the skin is dry again.
• Natural antiseptic properties. Salt and iodine have natural antimicrobial effects. For certain bacteria associated with skin conditions, such as Staphylococcus aureus, a common cause of folliculitis and impetigo, the salty environment is particularly unfavourable and helps inhibit bacterial growth. Clinical studies have also demonstrated changes in the skin microbiome of patients with atopic dermatitis undergoing Dead Sea climatotherapy, including a reduction in Staphylococcus and Streptococcus species."

However, the effects of seawater on the skin microbiome are not the same for everyone. They vary considerably depending on the skin's condition before exposure.

How the Sea Affects Oily and Acne-Prone Skin

"The combined effect of sunlight and seawater can:

• dry out inflamed acne lesions such as papules and pustules;
• reduce the number of certain microorganisms involved in acne development.

Salt also acts as a mild natural exfoliant, helping to unclog pores. However, it is important to remember that sun exposure can worsen non-inflammatory (retentional) acne, including both comedonal and microcystic acne.

The period after returning from holiday can also be problematic. If the skin becomes excessively dehydrated by saltwater and is not adequately moisturised afterwards, a so-called rebound effect may occur. In an attempt to compensate for dryness, the skin may produce even more sebum, potentially triggering a flare-up of acne.

For this reason, acne treatments should be carefully adjusted during the summer months and always combined with appropriate sun protection," Dr. Guanziroli explains.

How the Sea Affects Dry, Sensitive or Dermatitis-Prone Skin

"When the skin microbiome is already imbalanced or the skin barrier is compromised, saltwater can become irritating. Its osmotic effect draws water out of the skin, reducing its natural hydration levels. This may lead to:

• burning or stinging sensations;
• redness;
• increased vulnerability of the skin barrier to external aggressors."

How can you enjoy the sea without disrupting your skin's natural defence system? The key is balance. There is no need to avoid seawater, but it is important to care for your skin properly once you come out of the water. Simple daily habits can help protect and restore the skin microbiome:

• Rinse with fresh water. This is the single most important step. Showering after swimming removes salt crystals from the skin. If left in place, these crystals continue to dehydrate the skin and can also act like tiny magnifying glasses under the sun, increasing the risk of sunburn and skin irritation.
• Choose a gentle cleanser. Non-foaming cleansers, cleansing oils, or soap-free cleansers (syndets) are preferable. These products cleanse the skin without stripping away its protective hydrolipidic film, helping preserve the beneficial bacteria that make up the skin microbiome.
• Restore hydration with the right ingredients. Applying an emollient moisturiser after showering is essential for rebuilding the skin barrier. Products containing ceramides help restore the skin's structure, while prebiotic ingredients such as inulin, galacto-oligosaccharides, or oat extracts selectively nourish beneficial bacteria, promoting recolonisation of the skin surface and helping rebalance its pH.

Sunscreen: Essential for Protecting the Skin Microbiome

Sun exposure is closely linked to the health of the skin microbiome.

• Moderate, protected sun exposure supports vitamin D production and has beneficial immunomodulatory effects, for example in people with psoriasis.
• Intense UV radiation and sunburn, on the other hand, can significantly disrupt the skin microbiome by reducing microbial diversity and weakening the skin's local immune defences.

For this reason, applying a broad-spectrum sunscreen with SPF 50+ is essential. It protects not only your skin cells but also the beneficial microorganisms that help keep your skin healthy.