The safety of a bronzer stick for acne-prone skin largely depends on the ingredients it contains. Some ingredients can clog pores and exacerbate acne, while others can be beneficial.

Ingredients to avoid in a bronzer, especially for acne-prone skin, include Isopropyl Myristate, Laureth-4, and Oleth-3. These are known to be comedogenic, meaning they can clog pores and potentially lead to breakouts.

On the other hand, ingredients like Salicylic Acid, Niacinamide, and Zinc Oxide can be beneficial for acne-prone skin. Salicylic Acid can help to unclog pores, Niacinamide can reduce inflammation, and Zinc Oxide can provide sun protection.

It's also important to consider the form of the bronzer. Cream or stick bronzers can sometimes be more comedogenic than powder bronzers. However, this isn't a hard and fast rule, and again, it comes down to the specific ingredients used.

Lastly, remember to always remove your makeup thoroughly at the end of the day to prevent pore-clogging and breakouts.

In conclusion, a bronzer stick can be safe for acne-prone skin, provided it contains non-comedogenic ingredients and is used properly. Always check the ingredient list and consider your individual skin's needs and reactions.