Methaemoglobinaemia

Can be inherited

Can be got from drugs and stuff

• heavy metals
• lidocaine
• dapsone
• co-trimoxazole
• chlorate
• sulphonamides
• nitrates / nitrites

Makes you look blue

This is because methaemoglobin doesn't bind oxygen and cyanosis results

Treatment is with (appropriately enough) methylene blue

image from wikipedia