I say, and with God's success: The condition for permitting tayammum due to illness is that using water results in illness, exacerbation of the illness, or a delay in recovery, as informed by a just Muslim doctor. Fear of harm is not a requirement; tayammum is permitted if water is sold at an exorbitant price, and the harm of exacerbating the illness is greater than the harm of the increased price. Therefore, tayammum is permitted for this reason; as Allah Almighty said: {And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and do tayammum.} An-Nisa: 43. Refer to: Sharh Al-Waqaya p. 105, Fath Bab Al-Inaya 1: 110, and Al-Tabeen 1: 235, and Allah knows best.