The Cosrx Real Fit Vitamin C Serum claims to brighten skin, fade dark spots, even skin tone, plump the skin, refine texture, hydrate and smooth fine lines and wrinkles without the harsh side effects (irritation and redness) of an ascorbic acid product.

Ingredients: Propolis Extract, Ascorbic Acid, Aronia Melanocarpa Fruit Extract, Hippophae Rhamnoides Extract, Butylene Glycol, 1,2-Hexanediol, Sodium Lactate, Water, Cassia Obtusifolia Seed Extract, Sodium Hyaluronate, Allantoin

The first ingredient is 60% propolis extract, a material made by bees that soothes the skin and has antioxidant properties. Cosrx says they added propolis instead of water to combat dryness caused by vitamin C (though water is added as the eighth of 11 ingredients). Ascorbic acid is the most researched form of vitamin C in skincare, but is unstable and can be irritating. Vitamin C can even skin tone, brighten, reduce fine lines, wrinkles and spots, firm the skin and defend the skin against free radicals and environmental stressors. This formula contains 23% ascorbic acid at 99% purity. Aronia Melanocarpa Fruit Extract (black chokeberry) and Hippophae Rhamnoides Extract are antioxidants, hydrating and have some vitamins and minerals and are said to increase the stability and efficacy of the vitamin C. Butylene glycol is a skin conditioning ingredient that can soften the skin. Sodium lactate is a humectant. Cassia Obtusifolia Seed Extract is an antioxidant, anti-inflammatory and helps redness. Allantoin is a soothing ingredient.

Directions: Apply 2 or 3 drops to clean skin. Store in a dark, cool (15 to 25oC) place. If redness or irritation occurs, use every other day until skin adjusts.

The vitamin c serum comes in a lidded bottle packaged with a dropper. On opening the container, there was a small puff of air that was released and air bubbles moving the surface; this happened the first few times when opening. Cosrx sent an email saying that since the vitamin C has 99% purity, it reacts to temperature changes during shipping and gas is generated inside the product; this can cause the lid to slightly open and leak (this happened to one of my bottles). The serum comes in a 20 mL bottle and is best before 2 months once opened. It has no scent other than a slight vitamin C smell. It has a liquid texture and is light yellow in color.

I have oily/combination skin and used the Real Fit vitamin C for 5 months, using 5 to 6 drops per use (2 to 3 did not seem like enough) for 5 months every morning.

I got no irritation, stinging or redness of the skin until after about a month of use. I tried it on dry skin and damp skin with no other changes to my routine. Some days my skin would be fine, a few days my skin got very red and irritated (after 30 to 60 seconds of application) and I wanted to wash it off, and some days just stung a bit. I did not find this to be a hydrating formula (some days my skin felt quite dry and I got flakiness around my nose and mouth) and other products layered on top did not feel as nice on the skin. It left a dry, sticky layer over the skin. Using this, my skin felt a bit more rough than usual and there was no plumping of the skin.

I keep my skin care in my closet, away from light, heat and humidity. Despite this, the vitamin C was very unstable and started turning darker yellow after a couple weeks, then turning dark yellow-brown at about 6 weeks (best before 8 weeks). I did not get through more than half the bottle (of any of the bottles I purchased) before I could not use it due to oxidation. I wonder if the air in the bottle caused it to oxidize faster than it should have. Likely a bottle with about half the product and a pump would be better, but the pump would have to be metered and very smooth with a liquid formula and would probably have increased cost.

After about 2 weeks of use, my skin looked generally brighter and was less oily.

Above, after 5 months of use, my complexion looks generally brighter and less congested. The splotch of hyperpigmentation does not look greatly improved, but some of the darker spots have faded.

The left side of my face has darker hyperpigmentation and I was surprised by how much the spots on my cheekbones had faded. This is more noticeable on this side of my face likely because the spots were darker and more defined than the right side.

The left photo shows general improvement in brightness, pores and hyperpigmentation. I have some fine lines on my forehead that I do not think are improved, but the brown spots over the far eyebrow have faded and my forehead looks less oily.

I am not sure if this is my imagination or not, but looking in the mirror, I thought my skin looked darker than normal (surprising since I used this over the fall and winter). A quick read of an article on labmuffin.com says that ascorbic acid turns into erythrulose, an ingredient in fake tanner that reacts to proteins in dead skin cells, causing darkening of the skin. This can be prevented if the ascorbic acid is used in a formula with vitamin E and ferulic acid, using an oil or cream after application of the vitamin C to protect it from the air (which I did, using The Inkey List's Peptide Moisturizer) or using it at night.

The Cosrx Real Fit Vitamin C Serum C23 faded hyperpigmented spots, brightened and generally improved the skin's complexion, but is not a formula I enjoyed using; it is sticky, drying, irritating, unstable, oxidized before I could get halfway through the bottle (a waste of product and money) and potentially darkened the skin. Despite the results, I would not repurchase.

Thanks for reading.