Astringent: What is it, Uses, Benefits

Astringents Introduction

Topical astringents are used to firm Up (tone) the skin.


A substance that controls or tightens tissue, thereby alleviating conditions such as diarrhoea, haemonhages and secretions is known as astringent.

Astringent is applied to skin, mucous membrane and does not destruct the tissue. It will cause constriction of capillaries and small blood vessels. Astringent acts as protein precipitant and arrest discharge by causing shrinkage of tissue.

Zinc Oxide and Calamine are astringents used in lotions, powders and ointments to relieve from itching and choping in various forms of dermatitis. Astringent helps to reduce oiliness e.g. excessive precipitation.

Astringents have bacteriostatic properties, though they are not generally used as antiseptics. The protein-precipitation brought about by astringent is ascribed to presence of metallic ions having large charge/ radium ratio of strong electrostatic fields.

The metal would form complex with various polar groups present on the protein or enzyme. This complexation of important functional group at active site of protein or an enzyme cause a drastic change in properties of the protein.


Astringent are used to treat diarrhoea, and also possess deodorant properties. Astringent promote healing process.

Read and Learn More Pharmaceutical Inorganic Chemistry Notes


Alum is both a specific and a class of chemical compound. The specific compound is the Hydrated Potassium Aluminium Sulfate (potassium alum) with the formula KA1(S04)2.12H2O.

More widely, alums are double sulphate salts, with the formula AM(SO4)2.12H2O, where A is a monovalent cation such as Potassium or Ammonium and M is a trivalent metal ion such
as Aluminium or Chromium (IE).

Alums are prepared by adding a hot, concentrated solution of either Potassium or Ammonium Sulphate to a hot solution of an equimolar proportion of Aluminium Sulphate and the alums get separate out.



Alum occurs as colourless, transparent, colourless crystals, white granules or powder. It has sweetish strongly astringent taste. Its crystals are sometimes opaque on the surface
due to formation of traces of basic salt.

It is freely soluble in water but slowly dissolves in glycerine and insoluble in alcohol. The aqueous solution is acidic to litmus.

On heating potash alum melts, it loses the water of crystallization below 200°C, forming a white residue of anhydrous aluminium sulphate and potassium sulphates. It is soluble in the water but insoluble in alcohol.


Complexometirc titration of aluminium is carried out 0.9gm is dissolved in the 20 ml of water. Each ml of 0.1N disodium edetate is equivalent to 47.44 mg of A1K.(SO4).12H2O

Official Test for Identity

  1. A solution of water gives the reactions characteristic of aluminium & sulphate.
  2. A small quantity of a solution in water is treated with sodium bicarbonate & filtered. The filterate gives the reactions of potassium.


Alum is used as an ingredient of some brands of toothpaste or powders. It is used in many subunits vaccines as a adjuvant to enhance the body’s response to immunogen. Vaccines
include hepatitis A, hepatitis B and DTAP.

It is used by pet owners to stem bleeding associated with animal injuries caused by improper nail clipping. It is used as a haemostatic agent, as mouth washes or gargles, as bladder irrigitations.

It is a powerful astringent. It is used in making lotions and douches. It has also been used as vaginal cleaning and deodrant preparations.

Zinc Sulphate

Chemical Formula:  ZnSO4.7H2O                      Molecular Weight: 287.54

Synonym : white Vitriol


It is prepared by boiling metallic Zinc with dilute Sulphuric Acid. A slight excess of zinc metal is used and the reaction is allowed to continue untill hydrogen gas evolves out.


The solution is filtered to separate unreacted Zinc, concentrated and crystallized.

It may also be prepared by the action of dilute Sulphuric acid on Zinc Oxide.


Chemical Properties

1) A white precipitate Zn(OH)2 is formed when zinc sulphate reacts with NaOH. The precipitate is solubilised in excess of NaOH.

Chemical Property Of ZINC SULPHATE


It occurs as colourless, transparent crystals or crystalline powder. It is odourless. Its taste is astringent and metallic. It is very soluble in water and freely soluble in glycerin. It efflorescenes in dry air.


An aqueous solution of ZnSO2 has been acidic to litmus, due to hydrolysis of the salt and is having pH of about 5. The solution has been acid to solution of phenol red and not acid to solution of methyl orange.


Since it is efflorescent, it should be stored in tightly closed non-metallic containers.


It is incompatible with alkali carbonates and hydroxides and with astringent infusions and decocations.


It is widely used as an astringent and in emetic (induces vomiting). A 0.25% aqueous solution is also used as an opthalmic astringents. It is used as reflex emetic especially in Narcotic
Poisoning (opium alkaloids poisoning). It has also been used internally as an emetic.

Astringents Short Answer Questions

Question. 1. Define Astringent.
Answer. Astringent is a substance that causes the contraction or shrinkage of tissue that dry up secretions.

Question.2. How do astringent act?
Answer. Astringent acts as protein precipitant.

Question.3. Name any two inorganic compounds that arc used as astringent?
Answer. Zinc Chloride, Alum, Zinc Sulphate.

Question.4. What Is the another name of Zinc Sulphate?
Answer. White Vitriol.

Question.5. What is the method of preparation of Zinc Sulphate?
Answer. Zinc Sulphate is prepared by the action of dilute sulphuric acid on zinc oxide.

preparation of Zinc Sulphate

Question.6. What are the pharmaceutical uses of Zinc Sulphate?
Answer. Zinc Sulphate is used as an astringent and in emesis. A 0.25% aqueous solution is also used as an opthalmic astringents.

Question.7. Write down the incompatibilities of zinc sulphate?
Answer. Zinc Sulphate is incompatible with alkali carbonates and hydroxides.

Question.8. What are the properties of Zinc Sulphate?

  1. It occurs as colourless, transparent crystals or crystalline powder.
  2. It is very soluble in water and freely soluble in glycerine.

Question.9. Write down any two pharmaceutical uses of Alum?

  1. Alum is used as an ingredient of some tooth paste or powders.
  2. It is a powerful astringent.
  3. It is widely used in vaginal cleansing and deodrant preparation.

Question.10. What is the taste of Alum?
Answer. It has sweetish strongly astringent taste.

Astringents Fill In The Blanks

1. An astringent is a drug which shrinks by……………………from their surfaces.

Answer: Protein precipitation

2. Commercially……… prepared by heating metallic zinc to bright redness in the presence of preheated air.

Answer: ZnSO4

3. ……………… used in narcotic poisoning which is also an inorganic astringent.

Answer: ZnSO4 (Zinc sulphate)

4. Astringent act as………………..

Answer: Protein precipitate

5. Astringent cause…………………of tissue.

Answer: Shrinkage or contraction

6. Alum is prepared by adding a hot cone, solution of………………. to a hot solution of…………… and it get separate out.

Answer: Ammonium sulphate, aluminium sulphate

7. ……………………… used as astringent.

Answer: Zinc sulphate, Alum

8. Topical astringents are used to………………………..

Answer: Firm up the skin

9. Chemical formula of Alum is………………………while of Zinc Sulphate is………………

Answer: AM(SO4)2.12H2O, ZnSO4

10. ZnS04 is externally used as…………………..

Answer: Astringent

Astringents Multiple Choice Questions

1. What is the effect of astringents on tissues?

  1. Contraction
  2. Both a) and b)
  3. Shrinkage
  4. None of these

Answer: Both a) and b)

2. How do astringents act?

  1. Lipid precipitant
  2. Bacterial inhibition
  3. Protein precipitant
  4. Enzymatic catalysis

Answer: Bacterial inhibition And Protein precipitant

3. What is the chemical formula of Alum?

  1. KA1(SO4)2.12H2O
  2. K2SO4.12H2O
  3. KSO4.2H2O
  4. K(SO4)2.12H2O

Answer: KA1(SO4)2.12H2O

4. Zinc sulphate is also known as

  1. White vitriol
  2. Red vitriol
  3. Blue vitriol
  4. Yellow vitriol

Answer: White vitriol

5. Which inorganic astringent is used in the treatment of nacrotic poisoning?

  1. Alum
  2. Zinc Sulphate
  3. Aluminium chloride
  4. Zirconium Sulphate

Answer: Zinc Sulphate

6. Zinc sulphate is prepared by the action of………. on Zinc Oxide.

  1. Conc. HCl
  2. Conc. HNO3
  3. Conc. H2SO4
  4. None of these

Answer: Conc. H2SO4

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