After retinol, vitamin C is the skincare ingredient I get the most questions about. There are so many products with vitamin C in them now, but serums continue to be my favorite way to enjoy the benefits of this antioxidant. As someone who deals with hyperpigmentation from acne, antioxidants are a key part of my skincare routine for a bright, even complexion.

But I have also fallen victim to the hype before and spent entirely too much money on vitamin C serums that broke me out, leaving behind new scars to deal with. If you need some help navigating all of the choices out there, here are five things to remember when shopping:

1. Consider your skin type.

As is the case when choosing any skincare product, you need to first look at your skin type and what your complexion needs. Vitamin C is most commonly used for brightening the skin and reducing hyperpigmentation caused by acne or other injuries like scars or sun damage. It also supports collagen production to firm the skin. Whether your skin is dry or oily, sensitive, acne-prone or calm will determine the type of vitamin C serum that will work best.

2. Explore the options.

The most common forms of vitamin C used in skincare products are ascorbic acid, ethyl ascorbic acid, sodium ascorbyl phosphate, ascorbic palmitate, tetrahexyldecyl ascorbate, retinyl ascorbate and magnesium ascorbic phosphate. The most stable of all of these are ascorbic acid and ethyl ascorbic acid while magnesium ascorbyl phosphate is reported to be the most gentle and suitable for sensitive skins. Dermatologists recommend starting with a low concentration, between 8 and 10%, and working up gradually to 20%.

3. Choose your formulation.

There are also different consistencies to consider when selecting a vitamin C serum. I don’t like oily serums. They can be pore-clogging and have led to some pretty awful breakouts and a lot of lost money. Water-based liquid or gel serums are my preferred formulation because they also layer nicely with other products. No matter the formulation, vitamin C serums can turn quickly if not stored properly. And no, you don’t need to run out and buy a skincare refrigerator—just look for either dark or opaque glass packaging or my personal favorite, an airless pump. Once the product darkens to a deep golden or brown color, it’s probably not doing much for you anymore.

4. Adjust the rest of your routine.

To get the full benefits of your serum, you need to find the right place for it in your skincare routine. Typically, vitamin C is recommended for daytime use because it doesn’t always play nicely with stronger acids or retinol (there are some exceptions). As an antioxidant, vitamin C supports the effects of SPF, which you should apply daily anyway. I usually apply mine after cleansing and toning (with a non-exfoliating toner) and before any moisturizer or sunscreen.

5. Be prepared to wait.

The true results of any skincare product will take weeks, if not months, to show. While I’ve noticed some improved radiance (i.e. glow) overall after a week or two with my favorite vitamin C serum, it takes at least three months for serious dark marks to begin fading. So as long as you’re not experiencing an adverse reaction like acne or a rash, stick with it for at least that long or one full bottle.

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