Taco seasoning and fajita seasoning are extremely similar with almost identical ingredients, but the proportions vary. Here’s the breakdown: 1. Taco seasoning only contains trace amounts of onion powder and garlic powder (about 75% less) because it’s expected to be cooked with fresh onions and fresh garlic.  2. Taco seasoning contains ground coriander for hints of earthy, tart, and sweet notes; fajita seasoning does not. 3. Fajita seasoning contains sugar because it’s expected to be combined with an acidic marinade; taco seasoning does not. 4. Store-bought fajita seasoning typically contains citric acid to mimic freshly squeezed lime juice; taco seasoning does not. You can achieve this same fresh pop with a fresh squeeze of lime juice at the end of cooking to avoid any additives.