To use these bottles, simply unscrew the lid and fill them with your gels, oils, lotions, or creams through the wide mouth. Then place the filled bottles in a standard bottle - warmer to keep the contents just above body temperature. Make sure the bottle - warmer you use is suitable for these 8 - ounce bottles. When it comes to maintenance, you can wash the bottles with mild soap and warm water after each use. Just don't expose them to temperatures higher than 200ºF as this may damage the heat - resistant HDPE plastic. Also, keep in mind that the bottle warmer is not included in this pack.