Disclosed is a dermal barrier composition which contains a hydrophilic polymer emulsion and a hydrophobic polymer emulsion. The dermal barrier composition is moisture activated, and remains inert until the hydrophobic and hydrophilic polymer emulsions contact a suitable substrate such as human skin. The dermal barrier composition is itself an emulsion, and can optionally contain a biocidal agent for antimicrobial and antiviral efficacy. The dermal barrier composition can also contain other active agents such as sunscreens, insect repellents and fungicides. The dermal barrier composition can be applied topically to skin, where it forms a protective or barrier layer against a number of pathogenic and chemical irritants.