TIA’M My Signature C Source (OST C20) | How to layer Vitamin C in your routine

Why do you need Vitamin C?

Vitamin C is a powerful anti oxidant which helps achieve brighter and even skin tone, it treats acne scars and hyper-pigmentation. It also has mild exfoliation properties which help in achieving even skin tone.

Vitamin C aka L Ascorbic Acid (will refer as LAA throughout the post) helps in collagen synthesis. Collagen is a protein which boosts skin elasticity and aids in reducing fine lines and also anti ageing.

About TIA’M!

The original OST C20 is now re-branded as TIA’M My Signature C source. Except for the name and package nothing else has changed. TIA’M is the sister company of COSRX.

Brand Claims:

TIA’M My Signature C Source delivers a multitude of complexion benefits for beautifully healthy skin. Pure Vitamin C refine, brighten, balance and tone skin for a radiant appearance.


A metallic orange box which has instructions and ingredients printed in Korean and English. The serum comes in a dark brown sealed bottle, they have provided a pipette/dropper which should be used after breaking the seal. The bottle has the brand label mentioning the product and storage instructions in English and Korean.

Quantity : 30 ml

Ingredients analysis:

Water, Ascorbic Acid, Alcohol, Sodium Lactate, Butylene Glycol, Glucose, PEG-60 Hydrogenated Castor Oil, 1, 2-Hexanediol, Phenoxyethanol, Sodium Hyaluronate, Bis-PEG-18 Methyl Ether Dimethyl Silane, Xanthan Gum, Diethoxyethyl Succinate, Ammonium Acryloyldimethyltaurate/VP Copolymer, Carthamus Tinctorius Flower Extract, Citrus Aurantium Dulcis, Glycerin, Zinc PCA, Panthenol, Niacinamide, t-Butyl Alcohol, Camellia Sinensis Leaf Extract, Beta-Glucan, Tocopheryl Acetate, Lecithin, Caprylic/Capric Triglyceride, Ubiquinone, Diisopropyl Adipate
This product contains alcohol. If you are allergic to alcohol, do a patch test before including it in your routine.

The Serum :

  • Smell : Smells like orange flavored cough syrup, it’s a faint scent, it’s not bothersome at all!
  • Texture : Liquid, the viscosity is more like an essence.
  • Appearance : The most important factor, make sure the serum is clear to pale yellow in color. If it’s turning dark yellow or even orange discard the serum as it’s oxidized.

In the image below, you can see some crystalline formation around the bottle neck, this is a common occurrence and the product is still in a good condition.


How to use Vitamin C? (click here)

Since it is a lot of information, I have created separate post for that, click on the link above.


  • This serum is sticky, using it by itself will be uncomfortable but I didn’t face any discomfort because I had several layers of essence/creams after this step so my skin feels normal (as in not sticky).
  • Vitamin C gets oxidized easily, it’s quite difficult to formulate a stable 20% LAA hence it’s required that you use it soon after opening, 3-4 months span. Keep the bottle in the refrigerator. Discard once the serum turns a dark yellow or orange.
  • Vitamin C makes your skin sensitive to light, so it’s best to use it only at night and the next morning use a cleanser to wash it off and don’t forget your sunscreen. (later don’t come crying saying you got a sunburn).
  • Incorporating vitamin C in my routine was quite tricky because it isn’t friendly with many ingredients. I was extra cautious with my night routine because when used with proper care this product is a boon.

I started using this product on November 23, 2017 and I’m writing this post exactly a month later.

First 7 days:

Since I’m a daredevil, I never mixed it with a toner and I applied 3-4 drops onto my face. But I did patch test and I didn’t have any reactions. The serum didn’t burn me but it’s recomended to mix it with a toner if you have very sensitive skin (if you have extremely sensitive skin, opt for a serum with less LAA concentration). After two days I noticed that my skin was quite bright. A week later I noticed some stubborn scars were becoming light (they didn’t magically vanish but I could see that they were lighter than before).

Day 8 – Day 21:

The luminous effect on my face continued and my skin was feeling a lot better and bright with the pigmentation around my mouth also becoming lighter. By now I was generous with the application, I was using 5-6 drops for my face and neck.

But my stupidity kicked in during the second week. I forgot to apply sunscreen and I went bare-faced for a morning walk in the park nearby. And in the next 20 mins I had to come back crying to my mommy saying I got a sun burn. I slathered my favorite snail mucin, my HG Cosrx Snail Mucin to calm down any irritation. I had a red spot, just one but a bad one which will now remind me to never step out of my home without a sunscreen.

Day 22 – Day 30 :

With some extra care, I was able to treat the burn in a couple of days and my skin calmed the hell down at last. By now my acne scars have reduced a lot. It didn’t eliminate them completely but it has done a great job, much better than any other product I have used so far.

But it gave my skin a glow and brightness, it is no longer dull. My skin feels much healthy and it has evened my skin tone as well.

By Day 30 I noticed that I have hit the plateau effect. Plateau effect is where a product is no longer working for me, in skin language it means “Time for a new product.” My skin by now has shown the maximum improvement it can with 20% LAA and it means I should either opt for something with more LAA concentration or use another serum which can treat some other concerns.


  1. The quantity is perfect, a 30 ml bottle lasts you about two months when used daily. Since the product gets oxidized in 3-4 months after opening it is best to use it as fresh as it comes.
  2. The package is small and sturdy bottle, comes with a dropper which makes it easy to apply and also hygienic.
  3. Lives up to all it’s claims- brightening, even tone and does give a healthy radiant skin.
  4. Visible immediate results.
  5. No breakouts.


  1. Storing this is a problem, since it has to be refrigerated.
  2. Carrying this during travels can be tricky, I never threw away it’s carton and used it to store this while traveling.
  3. It is sticky when used by itself.
  4. It has a short life span after which it gets oxidized and loses it’s potency.

Note : The plateau effect is unique, what happened after one month to me can happen after 45 days or even better you might not even face it, alway remember that everyone’s skin is unique and your mileage may vary.

Would I recommend?

Definetely. It’s a must buy. 5/5

Where to get it from?

I bought mine from Wishtrend. It’s also available on Jolse, Beautynetkorea and Yesstyle.

This review is not sponsored, I purchased the product and all views are my own.

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