Custom Taxonomy and archive pages

I have a custom two custom taxonomies one called design_tag (tags) & one called design_category (category).

They are both used for the custom post design.

When I try and test for which one is active (in archives.php) using
<?php if (is_tax( ‘design_tag’)); echo ‘design tag’; ?>
<?php if (is_tax( ‘design_category’)); echo ‘design category’; ?>
both lines are output.

What should I be using ?