Astringent – Pharmaceutical Inorganic Chemistry B. Pharma 1st Semester



Learning Objectives

At the end of this lecture, the student will be able to:

• Define astringent

• Explain the monograph analysis of:

 Zinc sulphate

 Potash alum


• The word “astringent” derives from Latin adstringere, meaning “to bind fast”

• Definition: Astringent is a drug that reacts chemically with cellular proteins producing limited coagulation which is accompanied with shrinkage of body tissues

• Astringent protects from external irritation and reduces cellular permeability

• It also possesses local styptic and local antiseptic actions

 Astringent medicines cause shrinkage of mucous membranes or exposed tissues and are often used internally to check discharge of blood serum or mucous secretions

 This can happen with a sore throat, hemorrhages, diarrhea, or with peptic ulcers.  Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin

 Acne sufferers are often advised to use astringents if they have oily skin

Uses of astringents:

• Cleaning the face and preventing Acne Breakouts

• Stopping bleeding

• Relieving the discomfort and itching of insect bites, minor abrasions and Athlete’s foot

• Haemorrhoids

Benefits of Astringents

  • Pore Minimization: Astringents can make your pores appear smaller, giving your skin a smoother texture.
  • Oil Control: They help regulate excessive oil production, preventing acne and breakouts.
  • Toning Effect: Astringents can tighten the skin, reducing sagging and promoting a firmer appearance.
  • Refreshment: Astringents leave your skin feeling refreshed and rejuvenated.

Types of Astringents

Astringents come in various forms, and they can be categorized into two main types:

Topical Astringents vs. Oral Astringents

Topical astringents are applied directly to the skin, while oral astringents are taken internally. In this article, we’ll primarily focus on topical astringents and explore two specific examples: zinc sulphate and potash alum.

How to Use Astringents

Using astringents effectively is crucial for achieving the best results. Here’s how to incorporate them into your skincare routine:

  • Cleanse your face thoroughly.
  • Apply the astringent using a cotton ball, moving in upward motions.
  • Allow it to dry before applying moisturizer.

Monograph of zinc sulphate

Name: zinc sulphate

Chemical formula: ZnSO4, 7H2O

Molecular weight: 287.5

Standards: Zinc Sulphate contains not less than 99.0 per cent and not more than 104.0 per cent of ZnSO4, 7H2O

Method of Preparation:

Zn + H2SO4 + 7H2O à ZnSO4 7H2O + H2

Properties of zinc sulphate:


• A Colourless, transparent crystals or a white, crystalline powder

• Odourless

• Efflorescent

Solubility: Very soluble in water and glycerine and insoluble in alcohol

Test for purity

• Appearance of solution

• Chlorides

• Arsenic

• Iron

• Acidity/Alkalinity

Assay Principle

Complex metric, Direct titration

ZnSO4 + 2CH3COOH à Zn (CH3COOH)2

Zn (CH3COOH)2 + di Na EDTA à Zn EDTA complex

Indicator: xylenol orange triturate

Buffer: hexamine

Titrant: Di sodium EDTA

Colour change: violet pink- yellow

Storage: Store protected from moisture, in non-metallic containers

Medicinal uses:

• Astringent

• Emetic

Monograph of Potash alum

Name: Potash alum

Chemical formula: KAL(SO4)2.12H2O

Molecular weight: 474.4

Standards: It contains not less than 99.5 per cent

Method of Preparation:

K2SO4 + Al2(SO4)3 + 24H2O à KAL(SO4)2.12 H2O

Properties of Potash alum:


• A Colourless, transparent crystals or a white, crystalline powder

• Sweet astringent taste

• Heated to 200oC, loses its water of crystallisation and becomes anhydrous

Solubility: Very soluble in water and insoluble in alcohol

Test for purity

• Heavy metals

• Zinc

• Arsenic

• Iron

• Ammonium salt

Storage: Store in a well closed containers

Medicinal uses:

• Astringent and antiseptic

• Due to its protein precipitation used in the preparation of toxoids

• Astringents: protein precipitants

• Zinc sulphate: Is prepared by adding sulphuric acid on metallic zinc, assayed by complexometric direct titration and medicinally used as astringents and emetic

• Potash alum: used as astringent, double salt, used for water purification

Frequently Asked Questions (FAQs)

  1. Are astringents suitable for all skin types? Astringents are generally suitable for oily and combination skin. Individuals with dry or sensitive skin should use them sparingly.
  2. Can astringents cause skin dryness? Yes, overuse of astringents can lead to skin dryness. It’s essential to follow the recommended usage guidelines.
  3. Do astringents help with acne? Astringents can be beneficial for acne-prone skin, as they help control oil and minimize pores.
  4. Can I use astringents daily? It’s advisable to use astringents in moderation, typically once or twice a day.
  5. Are astringents safe during pregnancy? Consult with a healthcare professional before using astringents during pregnancy to ensure safety.

Also, Visit:

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