Operations That Don't Invoke Triggers

Some operations don’t invoke triggers.

Triggers are invoked for data manipulation language (DML) operations that the Java application server initiates or processes. Therefore, some system bulk operations don't invoke triggers. Some examples include:

Cascading delete operations. Records that did not initiate a delete don't cause trigger evaluation.
Cascading updates of child records that are reparented as a result of a merge operation
Mass campaign status changes
Mass division transfers
Mass address updates
Mass approval request transfers
Mass email actions
Modifying custom field data types
Renaming or replacing picklists
Managing price books
Changing a user's default division with the transfer division option checked
Changes to the following objects:
- BrandTemplate
- MassEmailTemplate
- Folder
Update account triggers don't fire before or after a business account record type is changed to person account (or a person account record type is changed to business account.)
Update triggers don’t fire on FeedItem when the LikeCount counter increases.

Inserts, updates, and deletes on person accounts fire Account triggers, not Contact triggers.

Note

The before triggers associated with the following operations are fired during lead conversion only if validation and triggers for lead conversion are enabled in the organization:

insert of accounts, contacts, and opportunities
update of accounts and contacts

Opportunity triggers are not fired when the account owner changes as a result of the associated opportunity's owner changing.

The before and after triggers and the validation rules don't fire for an opportunity when:

You modify an opportunity product on an opportunity.
An opportunity product schedule changes an opportunity product, even if the opportunity product changes the opportunity.

However, roll-up summary fields do get updated, and workflow rules associated with the opportunity do run.

The getContent and getContentAsPDF PageReference methods aren't allowed in triggers.

Note the following for the ContentVersion object:

Content pack operations involving the ContentVersion object, including slides and slide autorevision, don't invoke triggers.
Content packs are revised when a slide inside the pack is revised.
Note
Values for the TagCsv and VersionData fields are only available in triggers if the request to create or update ContentVersion records originates from the API.
You can't use before or after delete triggers with the ContentVersion object.

Triggers on the Attachment object don’t fire when:

the attachment is created via Case Feed publisher.
the user sends email via the Email related list and adds an attachment file.

Triggers fire when the Attachment object is created via Email-to-Case or via the UI.

Apex Developer Guide

Operations That Don't Invoke Triggers