Henna materials are used in the cosmetics industry. This OG alerts visiting staff that exposure to the henna dust may cause employees to become immunologically sensitised and develop occupational asthma. Some sources of henna may contain castor bean which is very toxic.
Henna is a generic name given to certain imported hair colouring agents of plant origin. A number of types have been identified, such as neutral henna (Lawsonia alba), Sedra henna (Acacia), red henna (Lawsonia inermis), Egyptian henna (Lawsonia inermis) and black henna (Lawsonia inermis and Indigofera tinctoria). They may contain various other plant materials.
Health problems have been found with exposure to the red, Egyptian and black hennas. A number of people handling/processing henna have developed allergic respiratory symptoms of breathlessness and wheezing after relatively short periods of exposure to the dust. Other henna types (neutral and Sedra henna) do not seem to convey the same properties.
As well as containing respiratory sensitisers, Castor bean (Ricinus communis) has been found in some supplies of henna. Castor beans also contain ricin and significant quantities of this substance have been found in some henna samples. Ricin is an extremely toxic substance that can cause severe acute reactions at low doses and can be lethal. It therefore presents a considerable potential risk to employees. Henna is normally supplied in plastic-lined hessian sacks of 50kg but the sack material is not thought to be implicated as a source of contamination.
Knowledge of the sensitisation potential of henna is limited and consequently importers and suppliers have been unaware of the risk. HSW Act s.6 information is therefore unlikely to provide such information to users. However, the trade association (the Cosmetics, Toiletry and Perfumery Association) is aware of the issue.
The requirements of the Control of Substances Hazardous to Health (COSHH) Regulations 2002 (as amended) apply to exposure to henna. Where reasonably practicable, exposure should be prevented and importers/suppliers should seek castor bean-free supplies, if these are available. Stringent procedures and practices should be adopted to ensure that exposure to henna dust is reduced to as low as reasonably practicable. Whilst the application of engineering controls and other techniques should substantially reduce the dust levels, air-fed RPE is also recommended for employees handling henna. Health surveillance will also be necessary.
Inspectors should be wary of any claims that heat-treating henna-containing materials to 100oC has destroyed its sensitising potential, as the success of this technique is unknown. However, such heat treatment will detoxify any ricin which may be present.
Workers in ancillary operations, HM Revenue & Customs, irradiation and sterilising plant operators, as well as those in sub-contracted packing, may also be at risk where there has been contact with henna.
Manufacturers and suppliers of henna-based products should be required to supply comprehensive HSW Act s.6 information to end-users of products such as hair colourants and shampoos; for example, hairdressers.
You should not go into areas where there is a respiratory risk unless you are sure the risk can be mitigated. Information for inspectors on dealing with the risk of their own exposure to hazardous substances (and asphyxiants) is available under 'hazardous substances' within the health topics of 'your health and safety' on HSE's Intranet.
It is unlikely that the half-mask respirators issued to visiting staff will give sufficient protection from castor bean aerosols.
Occupational hygiene unit, FOD SG Group 6