Azelaic Acid, the First 4 Weeks: A Sting Log and Split Schedule

Item	Detail	Basis
Status in Korea	“1,7-heptanedicarboxylic acid (azelaic acid), its salts and derivatives” is banned from cosmetics in Korea	MFDS drug safety portal (2021-08-24) · institution
Where it’s used	Used for acne in dermatology care as a 20% cream	Korean Dermatological Association · institution
Time frame in studies	The systematic review only included 43 randomized trials with at least 6 weeks of use	2023 PMID 37550898 · A
A precedent for logging sting	102 people recorded daily stinging and burning scores for each side of the face over 7 days	2009 PMID 19746764 · B
Guideline position	Classified as a conditional recommendation in the 2024 American Academy of Dermatology guideline	2024 PMID 38300170 · A

Why is azelaic acid banned in Korea?

Because the restricted cosmetic ingredient information on Korea’s Ministry of Food and Drug Safety (MFDS) drug safety portal lists “1,7-heptanedicarboxylic acid (azelaic acid), its salts and derivatives” as an ingredient banned from cosmetics in Korea (reference date 2021-08-24). The list doesn’t state a reason for the ban, so we won’t guess at one.

That’s why this article isn’t about adding azelaic acid to a cosmetic routine; it’s about how to log your first 4 weeks using it with a prescription from a clinic. If you’re in Korea and thinking about buying an “azelaic acid serum” from an overseas shopping site, it’s more accurate to first ask a doctor whether your skin needs a prescription. Rules differ by country, and in some countries dermocosmetics containing azelaic acid are sold, so if you live outside Korea, check how it’s handled where you are with a pharmacist or doctor.

What is azelaic acid made of?

Azelaic acid is a dicarboxylic acid found naturally in grains. The MFDS ingredient information lists its molecular formula as C9H16O4 and its CAS number as 123-99-9.

In Korean it goes by several transliterated names, but they all mean azelaic acid. Even if the name looks different on an ingredient list or a prescription leaflet, it’s the same ingredient, so stick to one name in your log.

What does azelaic acid 20% mean?

The Korean Dermatological Association explains that azelaic acid is used for acne in dermatology care as a 20% cream and tends to have fewer side effects than topical retinoids. A 2023 systematic review of 43 randomized trials on acne, rosacea and melasma (20 on rosacea, 16 on acne, 7 on melasma) also mostly covered the 20% strength.

There are studies of a 15% gel too. In a 2024 randomized trial following 40 adult women aged 25 to 44 for 6 months, the 15% gel was applied twice a day, and 15% of the gel group dropped out. Abroad, there’s also a 2023 Brazilian study in which 53 adult women whose acne had settled used a dermocosmetic containing azelaic acid for 16 weeks, but that’s a separate matter from Korea’s cosmetic rules.

How do you keep a sting diary in your first 4 prescribed weeks?

Every day, write one line: the time you applied it, the amount, and a sting score (0–10) five minutes later. In a 2009 study in which 102 people with rosacea using a 15% gel recorded stinging and burning scores for each side of the face for 7 days, the cumulative score dropped more on the side where a moisturizer was added.

That result comes from adding a moisturizer to a prescription gel, so it isn’t the effect of the moisturizer alone. Still, a “moisturizer added” column in your diary lets you show right away at your appointment which days stung less. In a 2004 study of 40 women with mild to moderate rosacea, 62.5% had a burning reaction to a lactic acid sting test, but no signs of barrier damage were found on water loss (TEWL) and stratum corneum hydration (corneometry) tests after 2 weeks on a 15% gel. Don’t decide to stop just because it stings; look at whether the score is going down or up.

How do you split days with salicylic acid or retinol products?

Don’t decide the split on your own; ask on the day you get the prescription and write down the answer. The 2024 American Academy of Dermatology guideline makes combining topical products with different mechanisms a good practice statement, but which combination to use and when is a decision for your doctor.

Three questions are enough in the exam room: whether to pause the salicylic acid toner or retinol serum you’ve been using for the first few weeks; if you bring them back, whether on the same day or different days; and above what sting score you should call. Copy the answers into the “days as instructed” column in the table below, and you won’t get confused even in weeks when your routine is thrown off, like exam weeks for students or shift work.

First 4-week sting diary

Week	Log daily	Days as instructed (example)	Also note	Show at the next visit
Prescription day	Strength, times per day, amount	Keep or pause current salicylic acid and retinol products	List of products you use now	—
Week 1	Time applied, sting 0–10 after 5 minutes	Days with azelaic acid only	Whether you added moisturizer	Day and area with the highest score
Week 2	Sting score, areas that turned red	(Fill in as instructed)	Days around your period, late work nights, sunny days	Whether it dropped from week 1
Weeks 3–4	Sting score, number of new bumps	Days you brought back your usual products	Names of products brought back	Score difference between days with and without them

Scoring at the same time every day matters. If you mix morning and night scores, day-to-day comparisons get blurry.

When should you call the clinic or see a dermatologist?

• If your sting score doesn’t drop or goes up after 1 to 2 weeks, or you get swelling or blisters, stop using it and contact the clinic that prescribed it.
• If you’re pregnant or planning a pregnancy, talk to a dermatologist before it’s prescribed.
• If deep bumps that hurt when pressed or breakouts that leave scars increase, move your next appointment up.
• If you’ve already been using a product bought from overseas and the redness won’t settle, stop the product and see a dermatologist.

Evidence behind this guide

• The MFDS drug safety portal (reference date 2021-08-24) classifies “1,7-heptanedicarboxylic acid (azelaic acid), its salts and derivatives” as an ingredient banned from cosmetics in Korea.
• A 2023 systematic review of 43 randomized trials (PMID 37550898) looked at 20 trials on rosacea, 16 on acne and 7 on melasma, mostly using the 20% strength for at least 6 weeks.
• In a 2009 study of 102 people with rosacea (PMID 19746764), the cumulative stinging and burning score over 7 days dropped more on the side of the face where a moisturizer was added to the 15% gel.