Should dental cavities keep getting worse even if you maintain excellent oral hygiene?

Yes: If you have active decay in your mouth it will continue to get worse until it is treated even with excellent oral hygiene.

Possibly: Other factors and conditions may be at play such as carbonated beverage usage, acid reflux, medicines that cause dry mouth and others may continue to contribute to dental cavities occuring and/or getting worse. Discuss your particular situation with your dentist to nail down the specific factors that you might be able to address.

Possible: You must have all cavities filled and then go from there. If you have done this and your dental professional tells you that your hygiene is excellent and you still get more decay, then: you must analyze the diet, sugar intake and frequency, and look for dry mouth. Decay only happens when bacteria get energy supply from sugar. The bacteria are with you for life, so you can only change your diet.

Good oral hygiene is Preventive Rx. But once cavity (infection) takes hold, hands-on Dental Treatment is mandatory as soon as possible. Easier, and less expensive, to treat a small infection than a large one.