Background: Preservatives are added to cosmetics and other consumer products to prevent microbial growth and product degradation. Many cosmetic preservatives are skin sensitizers and frequent causes of contact dermatitis. The use of preservatives may vary by country and/or region, according to legislation, and may be reflected in differences in the prevalence rates of preservative allergy worldwide. Objective: To examine the type and frequency of preservative use in cosmetics sold in Thai markets in metropolitan Bangkok, Thailand. Methods: Preservatives contained in 1000 different cosmetics sold in Thai markets were documented and analysed, based on the labelling of ingredients. Results: Most of the cosmetic and skincare products sold in Thai markets were international brands, with only a small proportion of cosmetic products being produced in Thailand. International brand cosmetics were more likely to contain non-formaldehyde-releasing preservatives than domestically produced brands. Isothiazolinone-based preservatives, which are responsible for the current increase in the prevalence of contact allergy, were found at a significant frequency in domestically produced, leave-on cosmetic products. Conclusion: Preservatives in cosmetics were significantly different according to source of production and type of cosmetics.