Beautyknot ~ My Skin Care Diary

Kiehl’s Powerful-Strength Line-Reducing Concentrate

Posted on: July 22, 2010



According to Kiehl’s, with continuous delivery of 10.5% pure vitamin C, the Powerful-Strength Line-Reducing Concentrate is to decrease the appearance of Marionette lines (the line from the corner of the mouth down to the chin or jaw bone), crow feet, and sub-orbital wrinkles, while improving skin texture and radiance. In short, this is anti-aging cum brightening.


I get very worried with the mild melasma on my cheek bones. Help… a new skin issue kept coming unwelcomely. I first started with DHC Vitamin C powder (Magnesium Ascorbyl Phosphate), but I actually wanted pure Vitamin C that was clinically-proven as an antioxidant, whitening agent and able to stimulate new collagen production at one time. So I decided to try this, best of all it is not steep-priced as many other potent cosmeceutical Vitamin C serums.


I have so much about this C concentrate to share with you, so please do bear with me this unusually long post.


Directions: Cleanse skin thoroughly prior to application. Apply over entire face twice daily (avoiding the eye area). Can be used alone or layered under your usual moisturizer. In case of contact with eyes, rinse them immediately. As the formula blends into the skin, you may experience a feeling of warmth. This sensation is normal.



The original color of this concentrate should be white. The sample that I tested at the Kiehl’s store on the day was in yellow like the color of Clinique Dramatically Different Moisturizing Lotion, obviously the vitamin C had been oxidized. Many of us have known that pure vitamin C product should be stored away from heat and light, most probably the heat of the shelves spotlights in the Kiehl’s store are responsible for the oxidization. I stored this inside refrigerator and the C concentrate is still remained in original white color after more than 7 months.


The packaging is excellent. Dark browny color to inhibit direct light exposure; plastic bottle is light and easy to handle; the pump-design reduces contamination risk to prolong its potency and it dispenses accurate amount; the pump stopper is helpful to avoid spillage in case it packed along with other stuff during a trip but I rather keep this in fridge when I went for trip, I certainly do not want to take the risk of getting oxidization.



It has very faint scent, basically scentless, which a big plus to me. The moisturizing consistency is feeling warm while spreading it onto skin, leaving a silicone-liked smooth feeling, together with few minutes mild redness. On the other hand, I think this concentrate works as an immediate cosmetical-wrinkle-filler too. While I was hesitant should I splurge on Shiseido Revital neck serum, this Vitamin C concentrate was able to deliver the same. Moreover, although the product direction had warned to avoid it on eye area, but it never irritated the eye and I actually used it directly under eye. It makes the undereye-expression-fine-lines simply visibly vanish and become less visible when laughing, of course for few hours only.


One thing to note, due to its silicone texture, it does not get along with certain texture such as fluidy gel. When I applied product like Estee Lauder ANR Synchronized Complex or Hada Labo Moist Essence together with this concentrate, it pilled if I did not spread the serum lightly (refer to below attached picture). So, avoid rubbing the skin after using this C concentrate.



I used 3~4 squirts for each application (face and neck) in the first month, after toning and before moisturizer/sunscreen. Later I realized using it liberally was too costly as it would not last more than 2 months then.  While using this generously, the highest compliment I can give to this product is, I hate makeup stealing the even-toned and healthy glowing complexion. Unfortunately my skin did not tolerated well (skin is prone to sensitivity) to highly concentrated Vitamin C in such frequent usage, together with the comedogenic issue (1~2 clog pores sometimes) because of the high-silicone texture.


I used 1~2 squirts on following months, mainly for targeted areas such as neck lines. After applied this day and night for the last 5 months……, honestly I am not certain if the neck line is really improved because it looked like it has been improved. Meanwhile, I also suspect the lighter and clearer skin tone affects the visual verdict. Perhaps answer will get clear up in long-term usage, perhaps I should have faith in the scientific research of Vitamin C, still, personally I believe the line will only become less visible at best by using topical-applied product.



It is too bad when I have to choose between this and my peptides serum which contains copper. I used them together in the beginning until I read excessive iron or copper can deactivate anti-oxidizing function of Vitamin C and may be, turn Vitamin C become potential pro-oxidant (source). Some advised 12 hours apart in between using Vitamin C and Copper-peptide, some disagreed because Vitamin C can stay in skin for more than 12 hours, some suffered adverse effect from Copper-peptide……, for peace of mind anyhow, I chose only one of them and that was the gentler peptides serum because I wanted something that can be used at anytime, including very fickle sensitive skin moment. This C concentrate could be irritating to unstable and inflamed skin due to the acidic nature of Vitamin C.


Besides all of above, Kiehl’s claims this is stabilized Vitamin C and can last for 12 months once opened. I performed a simple experiment (as stated below) to answer my doubt.


oöÖ Testing Ööo

(Jan – Jun 2010, approximately 22 – 38oC, Bangkok)


Capped the jar tightly all the times, it stored inside drawer, never exposed to sunlight, room temperature. After 80 days, it had turned to orange.


Opaque jar, capped tightly, room temperature, exposed to sunlight and heat in day time only, it turned to be slightly yellowish after 60 days, dark yellow after 80 days as shown in the picture.


Transparent jar, capped tightly, room temperature, exposed to sunlight in day time. The content started becoming a little yellowish after nearly a month. Darker yellow after 80 days as shown in the picture.


Covered the jar but never screwed the lid, it stored inside refrigerator. After 80 days, the original color remained.



From left to right: Exp1, Exp2, Exp4, Exp3

Comparing the intensity of oxidization of above observations on 80th day


Comparing the intensity of oxidization of above observations on 147th day



Needless to say, discard the product immediately when the color changed. I knew temperature and packaging will affect the stability of Vitamin C but Exp1 truly astonished me, which stored dark inside my dressing drawer with my other skincare items. That implied all my skincare items inside the drawer were not “safe” enough! Luckily I stored some skincare products (such as those amino-acid-based, natural oil, vitamin C) in fridge. Nonetheless, do note not every product is suitable to store in fridge, that depends on product formulation. Whereas Exp2 and Exp3 were placed in living room, with indirect sun exposure, yet they were oxidized slower than Exp1. The only reason I could think of, the better air ventilation of Exp2 & Exp3 and the sultry environment of Exp1 (both my room and living room are facing to West). Generally, comparing with my another Vitamin C experiment, personally I do agree Kiehl’s Powerful-Strength Line-Reducing Concentrate is more stable formulated.


Relatively gentle, simple formulated, enough Vitamin C concentration to be effective, imparts clearer skin tone, potentially improves wrinkle, an effective antioxidant, I am happy overall. Although it costs more for THB2900/50ml in Thailand, however Vitamin C product is not recommended to stock up, hence always get the fresh stock for best result. Mine is 3 months from the manufacturing date since it is second best-seller of Kiehl’s Thailand.


Rating:….)))      Excellent. Willing to buy again.



Propylene Glycol, Cyclopentasiloxane, Ascorbic Acid, Glycerin, Cetyl PEG/PPG-10/1 Dimethicone Crosspolymer, Lauroyl Lysine, Acrylates Copolymer, Adenosine.


Update on 18/8/2010:

When the content reached the bottom, I disassembled the pump and wanted to get the last bit of this concentrate, no waste ya.

It can be re-assembled later

Save the 0.01% of the concentrate




10 Responses to "Kiehl’s Powerful-Strength Line-Reducing Concentrate"


was this able to help in reducing under eye lines? i need something to reduce my under eye lines…

Hi erin,
At this time I wouldn’t be able to comment if it helps in reducing under eye lines as I was taking photo-rejuvenation treatments in the interim too, but I could tell you that my dynamic fine lines under eyes were still there, though I once noticed a remarkably improvement for those lines but I wasn]t certain what’s the actual factor that attributed to the improvement. It could be the gentle laser or products I used.

I’m thinking to purchase this for longer period trial next time to see if it can improve those lines independantly, meanwhile I’m also desperate to look for other clinical-proven effective eye care for this concern, such as retinol (I hope my eye area can tolerate the ingredient “b). If you have found any excellent one in future, please let me know. “v

[…] in above attached picture) has turned to yellow within a week. That immediately reminded me the oxidized colour of Vitamin C. Assuming the Magnesium Ascorbyl Phosphate (MAP, one of the Vitamin C derivatives) is the only the […]

[…] using Kiehl’s Over-Night Biological Peel and Powerful Strength Line-Reducing Concentrate for a week. Picture was taken on 7th Aug 2010 with […]

My Kiehl turn transparent color with slight original color as traces. What does that mean?

Hi Sunshine Koh,
I am not sure what is the real problem but I guess the product is probably too “old”. Please bring the product to Kiehls store or email to Kiehls for clarification.

i m thinking to get this as my Vit C serum, but do i have to keep this in fridge ??

Hi Simonne,
Nice to hear from you again.
I would say it is best to store in refrigerator if you are using it for more than 2-3 months else it is not a must if you store the serum in cool & dry place.

Vitamin C would degrade over time even without expose to heat and light, so make sure you get the manufacturing date as fresh as possible too. (“v)

I just bought this powerful strength line reducing concentrate without researching beforehand. then, i decided to spent sometimes to read the review and found your blog. i iLove the way you experiment and test the skin care product. Will start follow your blog. Keep blogging..

Thanks Bon Bon, hope it works great for you too (“v)

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July 2010

My apology

Hi, many things have been keeping my mind and time occupied these days, thus I need more time to response to all comments. Please bear with me, thank you.

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My Skin Profile

Sensitive, combination skin type, visible blood vessels, freckles, easily dehydrated, dry and having fine line undereye, occasional breakout, visible aging pores.



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