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Tiam My Signature C-Source Review | Courtesy Tiam (sister company of Cosrx!)

Annyeong, Everyone~
Fasting month/Ramadhan is coming to an end soon omg!
I feel like this year is the fastest Ramadhan month that I am going through.
Time. Flies. So. Fast.

Do you guys remember the popular OST C20 Vitamin C serum? If you never heard of it before you can check out my existing review on the product by clicking on the link below:

I loved that product, I considered it as my HOLY GRAIL and I am happy to be able to use it again this year!

This Tiam My Signature C-Source is the renewed version of the OST Original Pure Vitamin C20 Serum. This is because the brand OST C20 is rebranded to TIAM. As for the product, ONLY the product name has been changed while the ingredients and everything else stayed the same.

Disclaimer: I received this product from TIAM in exchange for my honest review.

Texts on the box still looks the same except for the name.

Same old ingredients~

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 (Safflower) Flower Extract, Citrus Aurantium Dulcis (Orange) Peel Oil, Glycerin, Zinc PCA, Panthenol, Niacinamide, t-Butyl Alcohol, Camellia Sinensis Leaf Extract, Beta-Glucan, Tocopheryl Acetate, Lecithin, Caprylic/Capric Triglyceride, Ubiquinone, Diisopropyl Adipate

The serum contains 20% of PURE VITAMIN C and it promises:
Skin brightening
Lighten acne scars
Eliminates blackheads
Evening of skin tone

​How to Use

1. After applying toner, spread the C Source on your face and lightly tap the area to be fully absorbed. 
2. If your skin is sensitive and if you use pure vitamin C product for the first time, you can mix 1~2 drops
of the source into your toner or moisturizer. 
3. Make sure to spread sun block when going outside, after applying the C source. 
5. After C Source, apply a moisturizing product for better effect.


1. It is best to keep this product out of direct sunlight and high temperatures, 
as this will damage the product. (TIP: To keep the product fresh longer, store it in the 
2. When you use this product, please avoid using any product that contains high levels of 
AHA, BHA and Retinol.​

For more information, head over to: My Signature C-Source


Same old packaging too~

Hard glass bottle and uses a pipette to dispense the serum. When the serum is new it is sealed with a cap in the box, then you replace it with the given pipette.

Second time having the serum and I never hard problems with the pipette.

I put the serum in the fridge after every time I use it so the serum residue on the outside tends to crystallize if you notice in the above photo, but it is actually nothing to worry about. It is already warned on the box that sediments will occur on the bottle neck. I like the warning. It feels that the company thoroughly tested the product before selling.

If the serum inside the bottle itself started to crystallize then the temperate in your fridge must have been too cold.

Due to the high content of vitamin C, the serum has to be refrigerated and not exposed to (direct) sunlight or warm temperature.


Again, same old consistency~

Colour: When the serum is fresh the colour will look clear. If you don't keep it in the fridge, it might just oxidizes quickly and become light orange to deep orange to brown in colour. As it oxidizes, the effect of the serum too will deteriorate. Thank goodness that it was still fresh when I received it. I get worried when I have a vitamin C product in shipment. I heard that it can oxidize if you don't finish it within 2~3 months. The content is 30ml.

Smell: smells like orangey syrups~

The serum is not as runny as water but it still runs. It is easy to spread and it dries sticky, this is why this product is required to wait 20~30 minutes until it has deeply absorbed into skin then only you can continue with the next skincare step. It can be time consuming so you have to spare some time if you want to add this into your routine.

How I apply it in my routine: after toner step and before implementing any other serums and essences. One full drop is enough for my whole face.

My Thoughts

ugh I should've taken a before and after photo! I have been using the serum for about 2 weeks now but inconsistency because there are times when I want to use my BHA treatments. I used to apply this serum twice everyday until I finish it, it lasted me close to two months when I use daily twice. This serum can't be mixed with products with high content of AHA/BHA/Retinol or else you'll get a bad reaction.

Though I hadn't been consistent with my vitamin C usage, I feel that the serum works! The above photo of my left and right cheeks were taken on 20th June 2017, about 2 weeks since I implemented the serum in my routine.


I feel that the serum indeed evens out my skin tone
➹ Lightens my existing acne scars
➹ Provides a decent glow to my highlighted areas
➹ Provides extra hydration in my skincare routine
➹ I don't observe any effects on blackheads, I don't really have them
➹ Doesn't break me out, I never experienced any irritation or negative effects


➹ Time consuming, have to wait 20~30 minutes for the stickiness to ease
➹ Have to use consistently before it expires
➹ Might not be travel friendly
➹ Have to keep it refrigerated

My Final Thoughts

The results in terms of lightening my acne scars would've been faster if I apply the serum like I used to~ which was twice daily, but anyway I still like this serum and I think that it is working on me, it is suited with my skin. This is far by the only vitamin C product that works on me.

I purchased my first bottle of this last year and when I finished with this one, I do plan on repurchasing it BUT I have a backup vitamin C in my stash which is from The Ordinary, so I'll be trying that one!

Where to Buy?

USD 14.99 + free shipping at Wishtrend*
USD 16.64 at StyleKorean*
USD 16.98 + free shipping at Jolse 

Links marked with * are affiliate links. I will gain a small commission if you made an order through the link. The commission will act as a donation to this blog and myself.

Thank you, TIAM for giving me the chance to use this serum (again) in exchange for my honest review! I enjoy using this serum so much.

Connect with me!

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  1. I really adore this serum I've been using it for 3-4 years now *-*

  2. Hi
    I want to buy the serum too. In wishtrend they have mentioned two products one with June 17 as the manufacturer date and other with August 17. The product lasts only 2-3 months.. is this after the package is opened?

    1. yes it is after opening so you should use it quickly before it oxidizes :)


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