Moisturizer

A moisturizer, also known as an emollient, is a cosmetic product designed to protect, hydrate, and lubricate the skin. In healthy skin, these tasks are handled by natural sebum. The term "emollient" comes from the Latin word *mollire*, meaning to soften.

Moisturizers work by influencing how much water evaporates from the skin, a process called transepidermal water loss. Normally, the skin balances its water content to keep its surface dry and flaky as a barrier against germs and dirt, while also preventing itself from becoming brittle. This moisture retention relies on a lipid layer between dead skin cells. The active ingredients in moisturizers are either occlusives or humectants. Occlusives create a water-repellent film on the skin’s surface to trap moisture; the thicker the occlusive layer, the better it works. For instance, ointments are more occlusive than creams, which are more occlusive than lotions. Normal water loss from skin is about 4–8 grams per square meter per hour, but a coating of petrolatum can cut that loss by 50–75% for several hours. The body’s own oils moisturize in the same way. Humectants, on the other hand, are water-loving substances that pull moisture from the air (when humidity is above 70%) to hydrate the skin. They can also draw water from deeper skin layers to the surface, which might reduce hydration deeper down if not paired with an occlusive. In practice, humectants are used alongside occlusives. Many moisturizers also contain water, which provides temporary hydration.

There are many types of moisturizers. Petrolatum is highly effective but often disliked for its greasy feel. Other common options include cetyl alcohol, cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, stearyl alcohol, castor oil, and various other oils. Moisturizers come as lotions, creams, ointments, bath oils, or soap substitutes. Mineral oils and waxes resist oxidation and rancidity, so they have largely replaced vegetable oils in emollients and topical medications. Cosmetic moisturizers may also contain antioxidants, ceramides, emulsifiers, fragrances, penetration enhancers, preservatives, and solvents. Some products claim anti-wrinkle or skin-enhancing effects, and many plant-based ingredients are marketed for skin benefits. Scientific evidence supports that certain ingredients—like retinol, vitamin C, melatonin, and protocatechuic acid—can improve skin. Recently, manufacturers have turned to plant-based emollients from renewable sources such as coconut oil, camellia seed oil, avocado oil, rapeseed oil, corn oil, soy oil, and castor oil. Choosing these botanical emollients is especially important for oily or acne-prone skin, where a non-comedogenic profile helps avoid clogged pores while still repairing the skin barrier. Current dermatological trends favor plant-derived formulas that balance essential fatty acids to hydrate without boosting sebum production.

Moisturizers treat skin conditions like psoriasis, ichthyosis vulgaris, xerosis, and itching from atopic dermatitis. They are also often used as bases or vehicles for topical medications, such as in Whitfield’s ointment, and are combined with humectants like salicylic acid and urea. They appear in sunscreens, antiperspirants, cleansers, shaving creams, aftershaves, and hair tonics, and are used in disposable diapers to prevent dry skin and diaper rash. For atopic dermatitis (eczema), moisturizers can improve skin comfort and reduce flare-ups. They can be applied as leave-on treatments, bath additives, or soap substitutes. Most leave-on products fall into categories from least to most greasy: lotions, creams, gels, or ointments. No single type is more effective than another, so people with eczema should choose based on age, affected body area, climate or season, and personal preference. However, daily moisturizer use in infants does not prevent eczema, and regular use on healthy infants is not advised.

Potential health risks include contact dermatitis from allergens or irritants in moisturizers. Over-moisturizing can disrupt the skin’s normal environment, allowing pathogens to overgrow and cause infections. For patients with dermatitis, moisturizers should not be applied more than once daily. Aromas or food additives in moisturizers can trigger immune reactions, including allergies. The term "hypoallergenic" is not regulated, and some pediatric products labeled as such have contained allergens. People with eczema are especially prone to allergic reactions because their damaged skin barrier lets preservatives bind to and activate immune cells. In 2014, the American Academy of Allergy, Asthma, and Immunology warned that natural lotions with food ingredients like oats, goat’s milk, cow’s milk, or coconut milk could cause problems.