SKIN BY MONICA | Cos De BAHA S4 Smooth skin
SKIN BY MONICA | Cos De BAHA S4 Smooth skin

S4 BHA Salicylic Acid 4% Exfoliant Serum - Acne Spot Treatment + Smooth Texture

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Salicylic Acid / Beta Hydroxy Acid, BHA, is a great ingredient to solve acne problems and smooth the surface of the skin. Because of its antibacterial effect it helps to prevent new acne from forming as well as clear existing ones by loosening the keratin plug that holds a blackhead intact in its sac.

This formula contains Niacinamide which is great for balancing the oil sebum for all skin types including dry skin. It is a great pore reducer too. When using any Niacinamide serum expect pores to appear larger for 4-5 days before it appears smaller. This happens as the debris trapped in each pore is cleared out and brought to the surface. Be patient and consistent and the skin will benefit with your efforts. 

This serum is particularly effective to help reduce under eye Keratosis Pilaris.
Use Nighlty 2-3 times weekly.

We recommend using Salicyclic Acid in the evenings right before bedtime as sensitivity may occur when applied during the day.

Be sure to drink your fluids and keep the area well nourished the following day to avoid a rebound effect as the skin will be drier than usual so the skin may over compensate and over produce oil to moisturise the area which in turn creates further clogging.


  • Helps fade hyperpigmentation
  • Reduce melanin production
  • Reducing redness
  • Reduce appearance of pores
  • Help new and existing acne
  • Reduce fine lines and wrinkles
  • Helps skin elasticity


  • Apply 1-2 drops after cleansing 
  • May use as spot treatment
  • Can be used as a skin surface smoother. Once a week only. 
  • Allow 20 seconds for the serum to absorb then apply moisturiser on top


  • Please note that all products can sometimes cause irritations for people with very sensitive skin. Please patch test before use.

  • Always test the product on a small area before using it. Ideally behind an ear or under the chin. 

  • Allow 24 hours to see if there is any adverse reaction towards the product. Stop using immediately if irritation occurs.

  • Avoid applying Salicylic Acid Serum before the skin is exposed to sunlight as it can cause the skin to become overly sensitive.

  • If this 4% formula is too strong then begin with the 2% formula.


  • Retinoids cream and serums - Yes
  • Malassezia, Fungal Acne, Folliculitis - Yes.
  • Pregnancy - Yes, From Trimester 3 onwards

  • Rosacea, Eczema, Psoriasis Skin types - Only if you really really must. Use with care with intense monitoring. Use only every other day

  • Roaccutane - No



  • Brand – Cos De BAHA
  • Volume - 30ml 1.0 fl oz
  • Product name – S4 Serum
  • Key Ingredients – Salicylic Acid 4%, Niacinamide
  • pH 3.4-3.6
  • Made in South Korea
  • Not tested on animals
  • Free from 6 harmful (Paraben, Gluten, Formaldehyde, Fragrance, Sulfate, Artificial Color)


*Aloe Barbadensis Leaf Extract, Cocamidopropyl Dimethylamine, Salicylic Acid (4%), 1,2-Hexanediol, Propanediol, Niacinamide, *Rosa Damascena Ext, Lavandula Angustifolia (Lavender) Flower Ext, Camellia Sinensis Leaf Ext, Melissa Officinalis Leaf Ext, Artemisia Vulgaris Ext, Hydroxyethylcellulose.