The effects of age and repeated cleaning-in-place (CIP) cycles on the hygienic properties of gasket materials used in the food industry were studied. The materials included in the study were EPDM (ethylene propylene diene monomer rubber), NBR (nitrile butyl rubber, also known as Buna-N), PTFE (polytetrafluoroethylene) and Viton (fluoroelastomer). The materials were exposed to prolonged alkali-acid treatments simulating repeated CIP cycles. In addition, materials aged in industrial dairy or brewing processes were examined. Mixed cultures of Bacillus thuringiensis and Pseudomonas fragi or Pantoea agglomerans and Pediococcus inopinatus were used as test organisms and the CIP was performed in an experimental test rig. The susceptibility to biofilm formation and the cleanability in CIP were assessed by the plate count method, epifluorescence microscopy, impedimetry and ATP bioluminescence measurements. Physical deterioration was observed both on experimentally aged materials and on materials aged in industrial processes, causing reduced cleanability. PTFE was most resistant to alkali-acid treatments and repeated CIP cycles. The hygienic properties of EPDM, NBR and Viton degenerated in repeated CIP cycles. The methods used for assessing cleanability are discussed.