What is the purpose limitation principle (Zweckbindung) under the Swiss DSG, and what happens if the purpose changes?

Question

Accepted Answer

The Swiss DSG requires personal data to be processed only for the purpose stated at collection, obvious from circumstances, or legally prescribed. Any change of purpose requires new consent.
The rule: Personal data may only be processed for the purpose that was:

Stated when the data was collected, OR
Apparent from the circumstances, OR
Prescribed by law.

What this means in practice: If a company collects your email address to send you order confirmations, they cannot start sending you marketing emails without getting separate consent. The original purpose was "order communication," not "advertising."
Medical example: Data collected for treatment may not simply be used for research or billing purposes. Treatment data stays bound to the treatment purpose unless the patient gives new consent or a separate legal basis exists.
When the purpose changes, the consent of the affected person must be obtained again. No shortcuts, no assumptions. This is one of the hardest principles for companies to follow because data is tempting to reuse.