The soap, the world's oldest brand, recently changed its formula - trebling the number of ingredients used - and making it 'smell and feel disgusting', according to some users.
A Facebook group campaigning for the return of the old soap was set up after customers realised that stocks were running dry in chemists and stores across the UK and they could only buy the new soap.
The group, called 'Bring Back The Original Pears Soap', says that the new soap - made in a factory in India - is 'radically different' to the old one.
Following a flood of complaints to owners Hindustan Unilever Ltd - which is based in Bombay - Pears bosses have agreed to bring the old soap back in March this year.
They even admitted that the new formula was 'not quite right at the moment'.
The old bar contained just eight ingredients - including rosemary and thyme extracts and also Pears Fragrance Essence - but these were ditched and replaced with 24 ingredients.
Among the new ingredients are;
* Sorbitol - a sugar substitute often used in diet foods and also as a thickener in toothpaste.
* Sodium Lauryl Sulfate (SLS) - A wetting agent used to allow the soap to glide across the skin. A health and safety warning about SLS states that it 'may worsen skin problems' and that it can cause oral sores.
* Linalool - A chemical found in plants used as a calming scent. A health and safety warning about Linalool states that it may cause allergic reactions such as eczema.
The soap was first produced in 1789 - 221 years ago - by Andrew Pears at a factory in central London, and was the world's first transparent soap and the first registered brand in the world.
But late last year the formula was changed - 'totally changing the smell and texture of the soap' and 'making it unrecognisable from the original'.
Users said the old amber bar, with its mild and spicy herbal fragrance, was destroyed and replaced with a bar of soap which smells 'very strongly of frankincense'.
The Facebook group, set up by Janice Halliwell - who has used the soap for more than 50 years - said: "The formula has changed considerably.
"The new packaging doesn't mention that it is hypo-allergenic nor does it claim to be non-comodgenic (does not block pores)."
She added: "Also, they've increased their packaging so that the soap inside the box is now in a cellophane wrap."
Alison Browning, a Facebook campaigner, said: "The new one is smaller, harder and smells too much of tea tree oil and there's too much packaging which isn`t very green. The old one was much, much better.
"If you start to use it it is almost gone after having two baths and washing with it. Also the new smell sets my asthma off its far too strong."
Tony Coultas said that he was boycotting the soap until it was changed back, adding: " I suggest that the only way to make a point is to boycott it."
Bridget Henderson agreed, adding: "I got two boxes of the new stuff. It looks and feels completely different, smells disgusting and the cellophane wrap is completely superfluous.
"Unless the reason why it is in the cellophane wrapping is to disguise the foul smell of carbolic if you're buying it in a shop, so you only realise your hideous mistake when you get to open it a couple of weeks later."
Neil Rutty, the Divisional Managing Director for Cert Brands - the UK firm charged with marketing Pears - admitted that the company had done and about-turn after a flood of complaints and said the old soap would be on supermarket shelves by March.
He said: "You will be pleased to hear that although some changes were made in October 2009, Unilever India have listened to their customers and are revising the product again and it will be much closer to the original by March this year."
He said he company had had 'numerous complaints' about the new formula, but said that since October 1.6m bars have been sold in the UK and that the new bars were more environmentally friendly.
He added: "It would appear that Unilever have not got the new formulation quite right at the moment, but from the samples I have seen we will be pretty much back to normal by March and consumers will only have the benefits of a greener product with improved moisturising qualities to enjoy.
"We appreciate that Pears consumers are very loyal and we will do everything to ensure they have a product that they can enjoy for many years to come."
The original listed ingredients are: Sodium Palmitate, Natural Rosin, Glycerine, Water, Sodium Cocoate, Rosemary Extract, Thyme Extract, Pears Fragrance Essence.
The listed ingredients of the new soap are: Sorbitol, Aqua, Sodium Palmate/stearate, Sodium Palmkernelate, Sodium Rosinate, Propylene Glycol, Sodium Lauryl Sulfate, PEG-4, Alcohol, Glycerin, Perfume, Sodium Chloride, Sodium Meta Bisulfite, Etidronic acid, Tetra Sodium EDTA, BHT, Cl 12490, Cl 47005, Benzyl Benzoate, Benzyl Salicylate, Cinnamal, Eugenol, Limonene, Linalool.
