Dyes and dyeing

Exposure to dyes

Dyes used in textile finishing have many different, complex chemical structures and there are many products in commercial use.  Uncontrolled exposure to some hazardous dyestuffs is clearly recognised as potentially harmful to health; but there are a very large number of dyes that have not been associated with any adverse health effects.  It is possible that, for a small number of these, adverse effects on health can occur but have not yet been detected; however, it is unlikely we will ever have complete knowledge of all the hazards of dyes.  So it is prudent to minimise exposure to dyes of all types, even if no adverse health effects are known.

Hazardous dyes

Some reactive dyes are recognised respiratory sensitisers.  Breathing in respiratory sensitisers can cause occupational asthma and, once a person is sensitised, re-exposure to even very small amounts of the same dye may result in allergic symptoms such as a runny or stuffy nose, watery or prickly eyes, wheezing, chest tightness and breathlessness.  Some dyes can cause allergic skin reactions.  Certain reactive, vat and disperse dyes are recognised skin sensitisers.

A small number of dyes, based on the chemical benzidine, are thought to cause cancer – there are substitutes for these dyes in textile use.

Other dyes may also present hazards to health.  It is essential to read the safety data sheet supplied with each hazardous product.


Adding sodium hydrosulphite, also known as sodium dithionite or 'hydros' to process vessels can cause serious injuries.  This generally happens when the substance has been added too quickly and has solidified into a plug.  The reaction is often so violent it causes the contents to erupt over the side of the vessel.  To avoid this, take these precautions:

Safe handling of dyestuffs

Identifying sources of exposure

The major route of personal exposure is inhalation of dye dust.  This can happen at many stages in the handling process, eg when opening dyestuff containers or cleaning spillages

Another exposure route is dyes being in contact with skin.  Harsh skin cleaning to remove colour may cause dermatitis

To reduce the risk to health from dyestuffs effectively, you need to identify, assess and control all sources of significant exposure.  Some sources of exposure typical to a textile dyehouse are given below

Preventing secondary exposure to dust from settled deposits

Opening and resealing containers and scooping powder

Dust clouds are raised:

Once dust is generated, the fine inhalable particles stay airborne for a long time.  Therefore, it is highly recommended that dispensing takes place under local exhaust ventilation - this usually means in the weighing booth.  To make this easier:

When refurbishing or planning a new facility, consider different options to the traditional method of storage.  These might include paternosters - rotary stores in which the shelves holding the dye drums are brought round to the weighing station.  The ventilated weighing station itself may be made mobile, guided on rails by the operator to the appropriate place on the shelf.  Robotic handling is employed in some dyehouses.

In some colour stores, dispensing all dyestuffs in the ventilated weighing room may not be practicable.  An example might include a commission dyehouse with a very large inventory of dyes, only a few grams of which are often needed at any one time.  In these circumstances:

Emptying dye containers and preparing for final disposal

The design of dye containers and liners can make removing residues and bagging waste difficult to do without creating a dust cloud.  Ideally, carry out these tasks under local exhaust ventilation and contact dye suppliers for their advice.

Dispensing liquids

If spills of liquid dye are allowed to dry out, they may release very fine particles of dust.  Reduce the likelihood of spillage by using automatic dispensers or carefully choosing transfer containers.  Clear up liquid spills straightaway.

Weighing out

Weighing out should always take place under local exhaust ventilation.

Metal scoops can be cleaned by carefully digging them into inert powder, eg Glaubers salt.  This cleans the scoops physically without wetting them or creating dust.

You may find the COSHH Essentials sheet RB2 Bag opening and weighing useful.  Although aimed at the rubber industry, some of the information is useful when handling dyestuffs.

Transfer of the weighed dyestuff to the next stage

Tipping dry dyestuff into a mixing vessel will create a dust cloud.  Weigh the dyestuff into a water soluble bag - the closed bag can be dropped into the mixing vessel and will then dissolve.

Manually mix the weighed dyestuff to a slurry or paste with water before transfer.  This could be done, conveniently, under the extraction provided for the weigh scale.  Take account of the fact that large containers of dye slurry will be heavy and difficult to handle.

Keep transit containers covered.

Dissolving the dye

Mixing vessels often need additions to be made and this is usually either at chest or shoulder height.  Chest height is preferred since there is less chance of a dust cloud being formed in the operator's breathing zone.  Also, manual handling problems will be reduced.

Do not start up high-speed mixers until any dry dye is wetted out and the stirrer blades are covered.  To prevent the emission of an aerosol of fine droplets during high-speed mixing, fit vessels with lids.  The lids should, preferably, have local exhaust ventilation.

Introducing live steam to an open vessel will create an aerosol.  Do not begin any steam heating until the dye solution has been diluted.

You may find some of the information in the COSHH Essentials sheet RB3 Mixing rubber ingredients useful.  Although produced for the rubber industry, a lot of the information is useful when handling dyestuffs.

Handling spillages and cleaning

Spillages and cleaning may be a very significant source of dust exposure if not adequately controlled.  Brushing up one small spillage can create a greater personal exposure than that received during the rest of the working day.  Therefore:

Changing filters in the extraction equipment

If this work is carried out in-house, it should proceed according to a written system of work covering the method of removing, handling and disposing of the contaminated filter and the standard of personal protective equipment to be worn. Respiratory protective equipment will be needed.  The suppliers of the extraction system should be able to advise you on the method of work.

Benzidine-based dyes

Benzidine is a carcinogen that can affect the bladder.  Dyes that are manufactured using benzidine as a parent compound contain very little benzidine in their finished form.  However, it can be regenerated under certain conditions where chemical-reducing agents act on the dye.  These conditions can occur during dyehouse processes such as dye stripping or following inhalation or ingestion.  Some benzidine-based dyes may themselves be carcinogenic.

In practice, benzidine-based dyes should not be used but they are not specifically prohibited.  Within textile finishing less hazardous substitutes have become readily available and there is no practical reason why they can't be used instead of benzidine-based dyes.  In the unlikely event of being able to show sufficient justification for their continued use, you should take the following additional measures:

Benzidine congener dyes are based on substances chemically similar to benzidine, such as o-tolidine and o-dianisidine, both of which are also carcinogens.  Find less hazardous substitutes for them, otherwise take these additional precautions with them.

Reactive dyes


Reactive dyes have a high degree of wet fastness because the reactive dye molecule fixes itself to natural materials such as cotton, silk, wool or leather by a strong chemical bond.  If reactive dyes are inhaled or ingested they can react in the same way in the body.  Sometimes this can affect the body's immune system.  Changes to the immune system may mean the next time a person is exposed to the same reactive dye, their body reacts very dramatically, even if the amount of dye involved is very small.  If this happens, the person is said to have become sensitised to that dye.

If the symptoms affect the lungs (often affecting the nose and eyes too) this is called respiratory sensitisation.  If the symptoms affect the skin, this is called skin sensitisation.  Reactive dyes may be respiratory and/or skin sensitisers, although skin sensitisation seems to be rare.

Evidence has shown that a number of reactive dyes have definitely caused respiratory sensitisation in the past.  However, there is no validated test procedure for assessing the potential of any individual reactive dye to cause respiratory sensitisation.  It is therefore prudent to handle all reactives as if they are respiratory sensitisers. This includes reactives used for dyeing wool.

The hazard to health from reactive dyes is only a concern before their application to the yarn or fabric. There is no known risk to anyone handling or wearing the dyed materials.

Symptoms of respiratory sensitisation

Symptoms of skin sensitisation

If someone exposed to reactive dyes displays one or more of these symptoms, you should investigate the possibility of sensitisation.  Be aware, though, that the symptoms could be caused by, eg exposure to irritant substances commonly used in dyehouses.

The symptoms may happen immediately on exposure to the particular dye, in which case it will be relatively easy to identify the connection.  However, a common pattern is that symptoms are delayed for several hours and are most severe in the evening or during the night.  When symptoms are delayed, the affected person might not realise that the ill health is linked with their work - their first indication might come when they have a holiday away from the workplace and realise that the symptoms they have been suffering from have improved or even disappeared.

Five facts to remember about sensitisation

  1. It is unpredictable.  A number of colour-weighers may work with reactive dyes under exactly the same conditions. Some may become sensitised; others may suffer no adverse health effects at all
  2. Most people who become sensitised to reactive dyes do so during the first two years of exposure but sometimes sensitisation happens years or even decades after starting to work with the dyes
  3. It is all or nothing: you are either sensitised to a reactive dye or you are not
  4. It is irreversible - you remain sensitised for life
  5. People become sensitised to a particular substance and symptoms occur only in response to that substance - if there is no exposure then there will be no symptoms.  However, a person who has become sensitised to one reactive dye may then be more likely to suffer adverse reactions to other dyes in the same chemical class.

What happens if exposure continues after a person has become sensitised?

If a person sensitised to a reactive dye continues to be exposed to it, their symptoms are likely to get worse. People who start off by reacting to the dye with a stuffy nose may go on to develop asthma.  Asthma attacks are likely to become progressively more severe. Once asthma is established, an attack may be triggered by things other than the reactive dye, such as tobacco smoke or cold air.  If this happens, the person may be left with occupational asthma for years after they stop working with the dye.

Some people who develop occupational asthma become so disabled that they cannot work again - not only with dyestuffs but in any job.  For some, a slow deterioration in their health caused by the occupational asthma means a shorter life expectancy.  In extreme cases, a sudden, severe asthma attack could kill them.

So, it is very important that you take all practicable steps to reduce employees' exposure to reactive dyes, reducing the risk of anyone becoming sensitised.  if someone does become sensitised, it should be recognised as quickly as possible so you can take steps to prevent their symptoms becoming worse.

Making workers aware of the risks

Individuals are in the best position to recognise any deterioration in their own health.  However, unless they are informed and regularly reminded of the risks of sensitisation, they may not attach any significance to the early symptoms.

Tell those who work with reactive dyes about:

Make sure that your training programme provides:

Everyone who may be exposed to reactive dyes should be given training.  Most obviously this will be the colour-weighers but it may include other dyehouse workers and laboratory and maintenance staff.  Line managers and first aiders also need to understand the risks.

Reducing exposure

In general, you should handle reactive dyes in the same way as other dyestuffs – see (link to handling dyestuffs safely) above.  Also consider the following:


Where technical demands require the use of a reactive dye, choose the least hazardous form of the dyestuff available.  The choice of low-dusting dyes such as those in granular, dust-suppressed or liquid form, can be a very important factor in reducing exposure.  Remember, however, that dust will be released if liquid spills are allowed to dry or granules become ground down.


The whole process of dispensing powdered and granular forms of reactive dye, not just at the weighing stage, should be carried out under local exhaust ventilation (LEV).  If the existing ventilation arrangements in your colour store will not accommodate dispensing dyes, you will need to provide a facility which does.  In the interim, people working within the colour store should wear suitable respiratory protective equipment (RPE).

More information about LEV and RPE can be found at the following links:

Health surveillance

Health surveillance is appropriate for anyone at risk of being sensitised to reactive dyes.  In practice, this means all colour-weighers and any maintenance staff involved in filter changing etc.  However, there may be more workers at risk of sensitisation – this will depend on who dissolves the dye and how this is done.

Check list

Check that you have ensured the following:

Updated 2021-05-11